THE DISTRIBUTION OF THE SEXES





Does the insect know beforehand the sex of the egg which it is about

to lay? When examining the stock of food in the cells just now, we

began to suspect that it does, for each little heap of provisions is

carefully proportioned to the needs at one time of a male and at

another of a female. What we have to do is to turn this suspicion

into a certainty demonstrated by experiment. And first let us find

out how the sexes are arranged.



It is not possible to ascertain the chronological order of a laying,

except by going to suitably-chosen species. Digging up the burrows of

Cerceris-, Bembex- or Philanthus-wasps will never tell us that this

grub has taken precedence of that in point of time nor enable us to

decide whether one cocoon in a colony belongs to the same family as

another. To compile a register of births is absolutely impossible

here. Fortunately there are a few species in which we do not find

this difficulty: these are the Bees who keep to one gallery and build

their cells in storeys. Among the number are the different

inhabitants of the bramble-stumps, notably the Three-pronged Osmiae,

who form an excellent subject for observation, partly because they

are of imposing-size--bigger than any other bramble-dwellers in my

neighbourhood--partly because they are so plentiful.



Let us briefly recall the Osmia's habits. Amid the tangle of a hedge,

a bramble-stalk is selected, still standing, but a mere withered

stump. In this the insect digs a more or less deep tunnel, an easy

piece of work owing to the abundance of soft pith. Provisions are

heaped up right at the bottom of the tunnel and an egg is laid on the

surface of the food: that is the first-born of the family. At a

height of some twelve millimetres (About half an inch.--Translator's

Note.), a partition is fixed, formed of bramble saw-dust and of a

green paste obtained by masticating particles of the leaves of some

plant that has not yet been identified. This gives a second storey,

which in its turn receives provisions and an egg, the second in order

of primogeniture. And so it goes on, storey by storey, until the

cylinder is full. Then a thick plug of the same green material of

which the partitions are formed closes the home and keeps out

marauders.



In this common cradle, the chronological order of births is perfectly

clear. The first-born of the family is at the bottom of the series;

the last-born is at the top, near the closed door. The others follow

from bottom to top in the same order in which they followed in point

of time. The laying is numbered automatically; each cocoon tells us

its respective age by the place which it occupies.



To know the sexes, we must wait for the month of June. But it would

be unwise to postpone our investigations until that period. Osmia-

nests are not so common that we can hope to pick one up each time

that we go out with that object; besides, if we wait for the

hatching-period before examining the brambles, it may happen that the

order has been disturbed through some insects' having tried to make

their escape as soon as possible after bursting their cocoons; it may

happen that the male Osmiae, who are more forward than the females,

are already gone. I therefore set to work a long time beforehand and

devote my leisure in winter to these investigations.



The bramble-sticks are split and the cocoons taken out one by one and

methodically transferred to glass tubes, of approximately the same

diameter as the native cylinder. These cocoons are arranged one on

top of the other in exactly the same order that they occupied in the

bramble; they are separated from one another by a cotton plug, an

insuperable obstacle to the future insect. There is thus no fear that

the contents of the cells may become mixed or transposed; and I am

saved the trouble of keeping a laborious watch. Each insect can hatch

at its own time, in my presence or not: I am sure of always finding

it in its place, in its proper order, held fast fore and aft by the

cotton barrier. A cork or sorghum-pith partition would not fulfil the

same purpose: the insect would perforate it and the register of

births would be muddled by changes of position. Any reader wishing to

undertake similar investigations will excuse these practical details,

which may facilitate his work.



We do not often come upon complete series, comprising the whole

laying, from the first-born to the youngest. As a rule, we find part

of a laying, in which the number of cocoons varies greatly, sometimes

falling as low as two, or even one. The mother has not deemed it

advisable to confide her whole family to a single bramble-stump; in

order to make the exit less toilsome, or else for reasons which

escape me, she has left the first home and elected to make a second

home, perhaps a third or more.



We also find series with breaks in them. Sometimes, in cells

distributed at random, the egg has not developed and the provisions

have remained untouched, but mildewed; sometimes, the larva has died

before spinning its cocoon, or after spinning it. Lastly, there are

parasites, such as the Unarmed Zonitis (Zonitis mutica, one of the

Oil-beetles.--Translator's Note.) and the Spotted Sapyga (A Digger-

wasp.--Translator's Note.), who interrupt the series by substituting

themselves for the original occupant. All these disturbing factors

make it necessary to examine a large number of nests of the Three-

pronged Osmia, if we would obtain a definite result.



I have been studying the bramble-dwellers for seven or eight years

and I could not say how many strings of cocoons have passed through

my hands. During a recent winter, in view particularly of the

distribution of the sexes, I collected some forty of this Osmia's

nests, transferred their contents into glass tubes and made a careful

summary of the sexes. I give some of my results. The figures start in

their order from the bottom of the tunnel dug in the bramble and

proceed upwards to the orifice. The figure 1 therefore denotes the

first-born of the series, the oldest in date; the highest figure

denotes the last-born. The letter M, placed under the corresponding

figure, represents the male and the letter F the female sex.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

F F M F M F M M F F F F M F M



This is the longest series that I have ever been able to procure. It

is also complete, inasmuch as it comprises the entire laying of the

Osmia. My statement requires explaining, otherwise it would seem

impossible to know whether a mother whose acts one has not watched,

nay more, whom one has never seen, has or has not finished laying her

eggs. The bramble-stump under consideration leaves a free space of

nearly four inches above the continuous string of cocoons. Beyond it,

at the actual orifice, is the terminal stopper, the thick plug which

closes the entrance to the gallery. In this empty portion of the

tunnel there is ample accommodation for numerous cocoons. The fact

that the mother has not made use of it proves that her ovaries were

exhausted; for it is exceedingly unlikely that she has abandoned

first-rate lodgings to go laboriously digging a new gallery elsewhere

and there continue her laying.



You may say that, if the unoccupied space marks the end of the

laying, nothing tells us that the beginning is actually at the bottom

of the cul-de-sac, at the other end of the tunnel. You may also say

that the laying is done in shifts, separated by intervals of rest.

The space left empty in the channel would mean that one of these

shifts was finished and not that there were no more eggs ripe for

hatching. In answer to these very plausible explanations, I will say

that, the sum of my observations--and they have been extremely

numerous--is that the total number of eggs laid not only by the

Osmiae but by a host of other Bees fluctuates round about fifteen.



Besides, when we consider that the active life of these insects lasts

hardly a month; when we remember that this period of activity is

disturbed by dark, rainy or very windy days, during which all work is

suspended; when lastly we ascertain, as I have done ad nauseam in the

case of the Three-horned Osmia, the time required for building and

victualling a cell, it becomes obvious that the total laying must be

kept within narrow bounds and that the mother has no time to lose if

she wishes to get fifteen cells satisfactorily built in three or four

weeks interrupted by compulsory rests. I shall give some facts later

which will dispel your doubts, if any remain.



I assume, therefore, that a number of eggs bordering on fifteen

represents the entire family of an Osmia, as it does of many other

Bees.



Let us consult some other complete series. Here are two:



1 2 3 4 5 6 7 8 9 10 11 12 13

F F M F M F M F F F F M F

F M F F F M F F M F M



In both cases, the laying is taken as complete, for the same reasons

as above.



We will end with some series that appear to me incomplete, in view of

the small number of cells and the absence of any free space above the

pile of cocoons:



1 2 3 4 5 6 7 8

M M F M M M M M

M M F M F M M M

F M F F M M

M M M F M

F F F F

M M M

F M



These examples are more than sufficient. It is quite evident that the

distribution of the sexes is not governed by any rule. All that I can

say on consulting the whole of my notes, which contain a good many

instances of complete layings--most of them, unfortunately, spoilt

through gaps caused by parasites, the death of the larva, the failure

of the egg to hatch and other accidents--all that I can say in

general is that the complete series begins with females and nearly

always ends with males. The incomplete series can teach us nothing in

this respect, for they are only fragments starting we know not

whence; and it is impossible to tell whether they should be ascribed

to the beginning, to the end, or to an intermediate period of the

laying. To sum up: in the laying of the Three-pronged Osmia, no order

governs the succession of the sexes; only, the series has a marked

tendency to begin with females and to finish with males.



The brambles, in my district, harbour two other Osmiae, both of much

smaller size: O. detrita, PEREZ, and O. parvula, DUF. The first is

very common, the second very rare; and until now I have found only

one of her nests, placed above a nest of O. detrita, in the same

bramble. Here, instead of the lack of order in the distribution of

the sexes which we find with O. tridentata, we have an order

remarkable for consistency and simplicity. I have before me the list

of the series of O. detrita collected last winter. Here are some of

them:



1. A series of twelve: seven females, beginning with the bottom of

the tunnel, and then five males.



2. A series of nine: three females first, then six males.



3. A series of eight: five females followed by three males.



4. A series of eight: seven females followed by one male.



5. A series of eight: one female followed by seven males.



6. A series of seven: six females followed by one male.



The first series might very well be complete. The second and fifth

appear to be the end of layings, of which the beginning has taken

place elsewhere, in another bramble-stump. The males predominate and

finish off the series. Nos. 3, 4 and 6, on the other hand, look like

the beginnings of layings: the females predominate and are at the

head of the series. Even if these interpretations should be open to

doubt, one result at least is certain: with O. detrita, the laying is

divided into two groups, with no intermingling of the sexes; the

first group laid yields nothing but females, the second, or more

recent, yields nothing but males.



What was only a sort of attempt with the Three-pronged Osmia--who, it

is true, begins with females and ends with males, but muddles up the

order and mixes the two sexes anyhow between the extreme points--

becomes a regular law with her kinswoman. The mother occupies herself

at the start with the stronger sex, the more necessary, the better-

gifted, the female sex, to which she devotes the first flush of her

laying and the fullness of her vigour; later, when she is perhaps

already at the end of her strength, she bestows what remains of her

maternal solicitude upon the weaker sex, the less-gifted, almost

negligible male sex.



O. parvula, of whom I unfortunately possess but one series, repeats

what the previous witness has just shown us. This series, one of nine

cocoons, comprises five females followed by four males, without any

mixing of the sexes.



Next to these disgorgers of honey and gleaners of pollen-dust, it

would be well to consult other Hymenoptera, Wasps who devote

themselves to the chase and pile their cells one after the other, in

a row, showing the relative age of the cocoons. The brambles house

several of these: Solenius vagus, who stores up Flies; Psen atratus,

who provides her grubs with a heap of Plant-lice; Trypoxylon figulus,

who feeds them with Spiders.



Solenius vagus digs her gallery in a bramble-stick that is lopped

short, but still fresh and green. The house of this Fly-huntress,

therefore, suffers from damp, as the sap enters, especially on the

lower floors. This seems to me rather insanitary. To avoid the

humidity, or for other reasons which escape me, the Solenius does not

dig very far into her bramble-stump and consequently can stack but a

small number of cells in it. A series of five cocoons gives me first

four females and then one male; another series, also of five,

contains first three females, with two males following. These are the

most complete that I have for the moment.



I reckoned on the Black Psen, or Psen atratus, whose series are

pretty long; it is a pity that they are nearly always greatly

interfered with by a parasite called Ephialtes mediator. (Cf. "The

Life of the Fly": chapter 2.--Translator's Note.) I obtained only

three series free from gaps: one of eight cocoons, comprising only

females; one of six, likewise consisting wholly of females; lastly,

one of eight, formed exclusively of males. These instances seem to

show that the Psen arranges her laying in a succession of females and

a succession of males; but they tell us nothing of the relative order

of the two series.



>From the Spider-huntress, Trypoxylon figulus, I learnt nothing

decisive. She appeared to me to rove about from one bramble to the

next, utilizing galleries which she has not dug herself. Not

troubling to be economical with a lodging which it has cost her

nothing to acquire, she carelessly builds a few partitions at very

unequal heights, stuffs three or four compartments with Spiders and

passes on to another bramble-stump, with no reason, so far as I know,

for abandoning the first. Her cells, therefore, occur in series that

are too short to give us any useful information.



This is all that the bramble-dwellers have to tell us; I have

enumerated the list of the principal ones in my district. We will now

look into some other Bees who arrange their cocoons in single files:

the Megachiles (Cf. Chapter 8 of the present volume.--Translator's

Note.), who cut disks out of leaves and fashion the disks into

thimble-shaped receptacles; the Anthidia (Cf. Chapters 9 and 10 of

the present volume.--Translator's Note.), who weave their honey-

wallets out of cotton-wool and arrange their cells one after the

other in some cylindrical gallery. In most cases, the home is the

produce of neither the one nor the other. A tunnel in the upright,

earthy banks, the old work of some Anthophora, is the usual dwelling.

There is no great depth to these retreats; and all my searches,

zealously prosecuted during a number of winters, procured me only

series containing a small number of cocoons, four or five at most,

often one alone. And, what is quite as serious, nearly all these

series are spoilt by parasites and allow me to draw no well-founded

deductions.



I remembered finding, at rare intervals, nests of both the Anthidium

and the Megachile in the hollows of cut reeds. I thereupon installed

some hives of a new kind on the sunniest walls of my enclosure. They

consisted of stumps of the great reed of the south, open at one end,

closed at the other by the natural knot and gathered into a sort of

enormous pan-pipe, such as Polyphemus might have employed. The

invitation was accepted: Osmiae, Anthidia and Megachiles came in

fairly large numbers, especially the first, to benefit by the queer

installation.



In this way I obtained some magnificent series of Anthidia and

Megachiles, running up to a dozen. There was a melancholy side to

this success. All my series, with not one exception, were ravaged by

parasites. Those of the Megachile (M. sericans, FONSCOL), who

fashions her goblets with robinia-, holm-, and terebinth-leaves, were

inhabited by Coelioxys octodentata (A Parasitic Bee.--Translator's

Note.); those of the Anthidium (A. florentinum, LATR.) were occupied

by a Leucopsis. Both kinds were swarming with a colony of pigmy

parasites whose name I have not yet been able to discover. In short,

my pan-pipe hives, though very useful to me from other points of

view, taught me nothing about the order of the sexes among the Leaf-

cutters and the cotton-weavers.



I was more fortunate with three Osmiae (O. tricornis, LATR., O.

cornuta, LATR., and O. Latreillii, SPIN.), all of whom gave me

splendid results, with reed-stumps arranged either against the walls

of my garden, as I have just said, or near their customary abode, the

huge nests of the Mason-bee of the Sheds. One of them, the Three-

horned Osmia, did better still: as I have described, she built her

nests in my study, as plentifully as I could wish, using reeds, glass

tubes and other retreats of my selecting for her galleries.



We will consult this last, who has furnished me with documents beyond

my fondest hopes, and begin by asking her of how many eggs her

average laying consists. Of the whole heap of colonized tubes in my

study, or else out of doors, in the hurdle-reeds and the pan-pipe

appliances, the best-filled contains fifteen cells, with a free space

above the series, a space showing that the laying is ended, for, if

the mother had any more eggs available, she would have lodged them in

the room which she leaves unoccupied. This string of fifteen appears

to be rare; it was the only one that I found. My attempts at indoor

rearing, pursued during two years with glass tubes or reeds, taught

me that the Three-horned Osmia is not much addicted to long series.

As though to decrease the difficulties of the coming deliverance, she

prefers short galleries, in which only a part of the laying is

stacked. We must then follow the same mother in her migration from

one dwelling to the next if we would obtain a complete census of her

family. A spot of colour, dropped on the Bee's thorax with a paint-

brush while she is absorbed in closing up the mouth of the tunnel,

enables us to recognize the Osmia in her various homes.



In this way, the swarm that resided in my study furnished me, in the

first year, with an average of twelve cells. Next year, the summer

appeared to be more favourable and the average became rather higher,

reaching fifteen. The most numerous laying performed under my eyes,

not in a tube, but in a succession of Snail-shells, reached the

figure of twenty-six. On the other hand, layings of between eight and

ten are not uncommon. Lastly, taking all my records together, the

result is that the family of the Osmia fluctuates round about fifteen

in number.



I have already spoken of the great differences in size apparent in

the cells of one and the same series. The partitions, at first widely

spaced, draw gradually nearer to one another as they come closer to

the aperture, which implies roomy cells at the back and narrow cells

in front. The contents of these compartments are no less uneven

between one portion and another of the string. Without any exception

known to me, the large cells, those with which the series starts,

have more abundant provisions than the straitened cells with which

the series ends. The heap of honey and pollen in the first is twice

or even thrice as large as that in the second. In the last cells, the

most recent in date, the victuals are but a pinch of pollen, so

niggardly in amount that we wonder what will become of the larva with

that meagre ration.



One would think that the Osmia, when nearing the end of the laying,

attaches no importance to her last-born, to whom she doles out space

and food so sparingly. The first-born receive the benefit of her

early enthusiasm: theirs is the well-spread table, theirs the

spacious apartments. The work has begun to pall by the time that the

last eggs are laid; and the last-comers have to put up with a scurvy

portion of food and a tiny corner.



The difference shows itself in another way after the cocoons are

spun. The large cells, those at the back, receive the bulky cocoons;

the small ones, those in front, have cocoons only a half or a third

as big. Before opening them and ascertaining the sex of the Osmia

inside, let us wait for the transformation into the perfect insect,

which will take place towards the end of summer. If impatience gets

the better of us, we can open them at the end of July or in August.

The insect is then in the nymphal stage; and it is easy, under this

form, to distinguish the two sexes by the length of the antennae,

which are larger in the males, and by the glassy protuberances on the

forehead, the sign of the future armour of the females. Well, the

small cocoons, those in the narrow front cells, with their scanty

store of provisions, all belong to males; the big cocoons, those in

the spacious and well-stocked cells at the back, all belong to

females.



The conclusion is definite: the laying of the Three-horned Osmia

consists of two distinct groups, first a group of females and then a

group of males.



With my pan-pipe apparatus displayed on the walls of my enclosure and

with old hurdle-reeds left lying flat out of doors, I obtained the

Horned Osmia in fair quantities. I persuaded Latreille's Osmia to

build her nest in reeds, which she did with a zeal which I was far

from expecting. All that I had to do was to lay some reed-stumps

horizontally within her reach, in the immediate neighbourhood of her

usual haunts, namely, the nests of the Mason-bee of the Sheds.

Lastly, I succeeded without difficulty in making her build her nests

in the privacy of my study, with glass tubes for a house. The result

surpassed my hopes.



With both these Osmiae, the division of the gallery is the same as

with the Three-horned Osmia. At the back are large cells with

plentiful provisions and widely-spaced partitions; in front, small

cells, with scanty provisions and partitions close together. Also,

the larger cells supplied me with big cocoons and females; the

smaller cells gave me little cocoons and males. The conclusion

therefore is exactly the same in the case of all three Osmiae.



Before dismissing the Osmiae, let us devote a moment to their

cocoons, a comparison of which, in the matter of bulk, will furnish

us with fairly accurate evidence as to the relative size of the two

sexes, for the thing contained, the perfect insect, is evidently

proportionate to the silken wrapper in which it is enclosed. These

cocoons are oval-shaped and may be regarded as ellipsoids formed by a

revolution around the major axis. The volume of one of these solids

is expressed in the following formula:



4 / 3 x pi x a x (b squared),



in which 2a is the major axis and 2b the minor axis.



Now, the average dimensions of the cocoons of the Three-horned Osmia

are as follows:



2a = 13 mm. (.507 inch.--Translator's Note.), 2b = 7 mm. (.273 inch.-

-Translator's Note.) in the females;



2a = 9 mm. (.351 inch.--Translator's Note.), 2b = 5 mm. (.195 inch.--

Translator's Note.) in the males.



The ratio therefore between 13 x 7 x 7 = 637 and 9 x 5 x 5 = 225 will

be more or less the ratio between the sizes of the two sexes. This

ratio is somewhere between 2 to 1 and 3 to 1. The females therefore

are two or three times larger than the males, a proportion already

suggested by a comparison of the mass of provisions, estimated simply

by the eye.



The Horned Osmia gives us the following average dimensions:



2a = 15 mm. (.585 inch.--Translator's Note.), 2b = 9 mm. (.351 inch.-

-Translator's Note.) in the females;



2a = 12 mm. (.468 inch.--Translator's Note.), 2b = 7 mm. (.273 inch.-

-Translator's Note.) in the males.



Once again, the ratio between 15 x 9 x 9 = 1215 and 12 x 7 x 7 = 588

lies between 2 to 1 and 3 to 1.



Besides the Bees who arrange their laying in a row, I have consulted

others whose cells are grouped in a way that makes it possible to

ascertain the relative order of the two sexes, though not quite so

precisely. One of these is the Mason-bee of the Walls. I need not

describe again her dome-shaped nest, built on a pebble, which is now

so well-known to us. (Cf. "The Mason-bees": chapter 1.--Translator's

Note.)



Each mother chooses her stone and works on it in solitude. She is an

ungracious landowner and guards her site jealously, driving away any

Mason who even looks as though she might alight on it. The

inhabitants of the same nest are therefore always brothers and

sisters; they are the family of one mother.



Moreover, if the stone presents a large enough surface--a condition

easily fulfilled--the Mason-bee has no reason to leave the support on

which she began her laying and go in search of another whereon to

deposit the rest of her eggs. She is too thrifty of her time and of

her mortar to involve herself in such expenditure except for grave

reasons. Consequently, each nest, at least when it is new, when the

Bee herself has laid the first foundations, contains the entire

laying. It is a different thing when an old nest is restored and made

into a place for depositing the eggs. I shall come back later to such

houses.



A newly-built nest then, with rare exceptions, contains the entire

laying of one female. Count the cells and we shall have the total

list of the family. Their maximum number fluctuates round about

fifteen. The most luxuriant series will occasionally reach as many as

eighteen, though these are very scarce.



When the surface of the stone is regular all around the site of the

first cell, when the mason can add to her building with the same

facility in every direction, it is obvious that the groups of cells,

when finished, will have the oldest in the central portion and the

more recent in the surrounding portion. Because of this juxtaposition

of the cells, which serve partly as a wall to those which come next,

it is possible to form some estimate of the chronological order of

the cells in the Chalicodoma's nest and thus to discover the sequence

of the two sexes.



In winter, by which time the Bee has long been in the perfect state,

I collect Chalicodoma-nests, removing them bodily from their support

with a few smart sideward taps of the hammer on the pebbles. At the

base of the mortar dome the cells are wide agape and display their

contents. I take the cocoon from its box, open it and take note of

the sex of the insect enclosed.



I should probably be accused of exaggeration if I mentioned the total

number of the nests which I have gathered and the cells which I have

inspected by this method during the last six or seven years. I will

content myself with saying that the harvest of a single morning

sometimes consisted of as many as sixty nests of the Mason-bee. I had

to have help in carrying home my spoils, even though the nests were

removed from their stones on the spot.



>From the enormous number of nests which I have examined, I am able to

state that, when the cluster is regular, the female cells occupy the

centre and the male cells the edges. Where the irregularity of the

pebble has prevented an even distribution around the initial point,

the same rule has been observed. A male cell is never surrounded on

every side by female cells: either it occupies the edges of the nest,

or else it adjoins, at least on some sides, other male cells, of

which the last form part of the exterior of the cluster. As the

surrounding cells are obviously of a later date than the inner cells,

it follows that the Mason-bee acts like the Osmiae: she begins her

laying with females and ends it with males, each of the sexes forming

a series of its own, independent of the other.



Some further circumstances add their testimony to that of the

surrounded and surrounding cells. When the pebble projects sharply

and forms a sort of dihedral angle, one of whose faces is more or

less vertical and the other horizontal, this angle is a favourite

site with the Mason, who thus finds greater stability for her edifice

in the support given her by the double plane. These sites appear to

me to be in great request with the Chalicodoma, considering the

number of nests which I find thus doubly supported. In nests of this

kind, all the cells, as usual, have their foundations fixed to the

horizontal surface; but the first row, the row of cells first built,

stands with its back against the vertical surface.



Well, these older cells, which occupy the actual edge of the dihedral

angle, are always female, with the exception of those at either end

of the row, which, as they belong to the outside, may be male cells.

In front of this first row come others. The female cells occupy the

middle portion and the male the ends. Finally, the last row, closing

in the remainder, contains only male cells. The progress of the work

is very visible here: the Mason has begun by attending to the central

group of female cells, the first row of which occupies the dihedral

angle, and has finished her task by distributing the male cells round

the outside.



If the perpendicular face of the dihedral angle be high enough, it

sometimes happens that a second row of cells is placed above the

first row backing on to that plane; a third row occurs less often.

The nest is then one of several storeys. The lower storeys, the

older, contain only females; the upper, the more recent storey,

contains none but males. It goes without saying that the surface

layer, even of the lower storeys, can contain males without

invalidating the rule, for this layer may always be looked upon as

the Chalicodoma's last work.



Everything therefore contributes to show that, in the Mason-bee, the

females take the lead in the order of primogeniture. Theirs is the

central and best-protected part of the clay fortress; the outer part,

that most exposed to the inclemencies of the weather and to

accidents, is for the males.



The males' cells do not differ from the females' only by being placed

at the outside of the cluster; they differ also in their capacity,

which is much smaller. To estimate the respective capacities of the

two sorts of cells, I go to work as follows: I fill the empty cell

with very fine sand and pour this sand back into a glass tube

measuring 5 millimetres (.195 inch.--Translator's Note.) in diameter.

>From the height of the column of sand we can estimate the comparative

capacity of the two kinds of cells. I will take one at random among

my numerous examples of cells thus gauged.



It comprises thirteen cells and occupies a dihedral angle. The female

cells give me the following figures, in millimetres, as the height of

the columns of sand:



40, 44, 43, 48, 48, 46, 47

(1.56, 1.71, 1.67, 1.87, 1.87, 1.79, 1.83 inches.--Translator's

Note.),



averaging 45. (1.75 inches.--Translator's Note.)



The male cells give me:



32, 35, 28, 30, 30, 31

(1.24, 1.36, 1.09, 1.17, 1.17, 1.21 inches.--Translator's Note.),



averaging 31. (1.21 inches.--Translator's Note.)



The ratio of the capacity of the cells for the two sexes is therefore

roughly a ratio of 4 to 3. The actual contents of the cell being

proportionate to its capacity, the above ratio must also be more or

less the ratio of provisions and sizes between females and males.

These figures will assist us presently to tell whether an old cell,

occupied for a second or third time, belonged originally to a female

or a male.



The Chalicodoma of the Sheds cannot give us any information on this

matter. She builds under the same eaves, in excessively populous

colonies; and it is impossible to follow the labours of any single

Mason, whose cells, distributed here and there, are soon covered up

with the work of her neighbours. All is muddle and confusion in the

individual output of the swarming throng.



I have not watched the work of the Chalicodoma of the Shrubs with

close enough attention to be able to state definitely that this Bee

is a solitary builder. Her nest is a ball of clay hanging from a

bough. Sometimes, this nest is the size of a large walnut and then

appears to be the work of one alone; sometimes, it is the size of a

man's fist, in which case I have no doubt that it is the work of

several. Those bulky nests, comprising more than fifty cells, can

tell us nothing exact, as a number of workers must certainly have

collaborated to produce them.



The walnut-sized nests are more trustworthy, for everything seems to

indicate that they were built by a single Bee. Here females are found

in the centre of the group and males at the circumference, in

somewhat smaller cells, thus repeating what the Mason-bee of the

Pebbles has told us.



One clear and simple rule stands out from this collection of facts.

Apart from the strange exception of the Three-pronged Osmia, who

mixes the sexes without any order, the Bees whom I studied and

probably a crowd of others produce first a continuous series of

females and then a continuous series of males, the latter with less

provisions and smaller cells. This distribution of the sexes agrees

with what we have long known of the Hive-bee, who begins her laying

with a long sequence of workers, or sterile females, and ends it with

a long sequence of males. The analogy continues down to the capacity

of the cells and the quantities of provisions. The real females, the

Queen-bees, have wax cells incomparably more spacious than the cells

of the males and receive a much larger amount of food. Everything

therefore demonstrates that we are here in the presence of a general

rule.



But does this rule express the whole truth? Is there nothing beyond a

laying in two series? Are the Osmiae, the Chalicodomae and the rest

of them fatally bound by this distribution of the sexes into two

distinct groups, the male group following upon the female group,

without any mixing of the two? Is the mother absolutely powerless to

make a change in this arrangement, should circumstances require it?



The Three-pronged Osmia already shows us that the problem is far from

being solved. In the same bramble-stump, the two sexes occur very

irregularly, as though at random. Why this mixture in the series of

cocoons of a Bee closely related to the Horned Osmia and the Three-

horned Osmia, who stack theirs methodically by separate sexes in the

hollow of a reed? What the Bee of the brambles does cannot her

kinswomen of the reeds do too? Nothing, so far as I know, can explain

this difference in a physiological act of primary importance. The

three Bees belong to the same genus; they resemble one another in

general outline, internal structure and habits; and, with this close

similarity, we suddenly find a strange dissimilarity.



There is just one thing that might possibly arouse a suspicion of the

cause of this irregularity in the Three-pronged Osmia's laying. If I

open a bramble-stump in the winter to examine the Osmia's nest, I

find it impossible, in the vast majority of cases, to distinguish

positively between a female and a male cocoon: the difference in size

is so small. The cells, moreover, have the same capacity: the

diameter of the cylinder is the same throughout and the partitions

are almost always the same distance apart. If I open it in July, the

victualling-period, it is impossible for me to distinguish between

the provisions destined for the males and those destined for the

females. The measurement of the column of honey gives practically the

same depth in all the cells. We find an equal quantity of space and

food for both sexes.



This result makes us foresee what a direct examination of the two

sexes in the adult form tells us. The male does not differ materially

from the female in respect of size. If he is a trifle smaller, it is

scarcely noticeable, whereas, in the Horned Osmia and the Three-

horned Osmia, the male is only half or a third the size of the

female, as we have seen from the respective bulk of their cocoons. In

the Mason-bee of the Walls there is also a difference in size, though

less pronounced.



The Three-pronged Osmia has not therefore to trouble about adjusting

the dimensions of the dwelling and the quantity of the food to the

sex of the egg which she is about to lay; the measure is the same

from one end of the series to the other. It does not matter if the

sexes alternate without order: one and all will find what they need,

whatever their position in the row. The two other Osmiae, with their

great disparity in size between the two sexes, have to be careful

about the twofold consideration of board and lodging. And that, I

think, is why they begin with spacious cells and generous rations for

the homes of the females and end with narrow, scantily-provisioned

cells, the homes of the males. With this sequence, sharply defined

for the two sexes, there is less fear of mistakes which might give to

one what belongs to another. If this is not the explanation of the

facts, I see no other.



The more I thought about this curious question, the more probable it

appeared to me that the irregular series of the Three-pronged Osmia

and the regular series of the other Osmiae, of the Chalicodomae and

of the Bees in general were all traceable to a common law. It seemed

to me that the arrangement in a succession first of females and then

of males did not account for everything. There must be something

more. And I was right: that arrangement in series is only a tiny

fraction of the reality, which is remarkable in a very different way.

This is what I am going to prove by experiment.





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