THE MOTHER DECIDES THE SEX OF THE EGG





I will begin with the Mason-bee of the Pebbles. (This is the same

insect as the Mason-bee of the Walls. Cf. "The Mason-bees": passim.--

Translator's Note.) The old nests are often used, when they are in

good enough repair. Early in the season the mothers quarrel fiercely

over them; and, when one of the Bees has taken possession of the

coveted dome, she drives any stranger away from it. The old house is

far from being a ruin, only it is perforated with as many holes as it

once had occupants. The work of restoration is no great matter. The

heap of earth due to the destruction of the lid by the outgoing

tenant is taken out of the cell and flung away at a distance, atom by

atom. The remnants of the cocoon are also thrown away, but not

always, for the delicate silken wrapper sometimes adheres closely to

the masonry.



The victualling of the renovated cell is now begun. Next comes the

laying; and lastly the orifice is sealed with a mortar plug. A second

cell is utilized in the same way, followed by a third and so on, one

after the other, as long as any remain unoccupied and the mother's

ovaries are not exhausted. Finally, the dome receives, mainly over

the apertures already plugged, a coat of plaster which makes the nest

look like new. If she has not finished her laying, the mother goes in

search of other old nests to complete it. Perhaps she does not decide

to found a new establishment except when she can find no second-hand

dwellings, which mean a great economy of time and labour. In short,

among the countless number of nests which I have collected, I find

many more ancient than recent ones.



How shall we distinguish one from the other? The outward aspect tells

you nothing, owing to the great care taken by the Mason to restore

the surface of the old dwelling equal to new. To resist the rigours

of the winter, this surface must be impregnable. The mother knows

that and therefore repairs the dome. Inside, it is another matter:

the old nest stands revealed at once. There are cells whose

provisions, at least a year old, are intact, but dried up or musty,

because the egg has never developed. There are others containing a

dead larva, reduced by time to a blackened, curled-up cylinder. There

are some whence the perfect insect was never able to issue: the

Chalicodoma wore herself out in trying to pierce the ceiling of her

chamber; her strength failed her and she perished in the attempt.

Others again and very many are occupied by ravagers, Leucopses (Cf.

"The Mason-bees": chapter 11.--Translator's Note.) and Anthrax-flies,

who will come out a good deal later, in July. Altogether, the house

is far from having every room vacant; there are nearly always a

considerable number occupied either by parasites that were still in

the egg-stage at the time when the Mason-bee was at work or by

damaged provisions, dried grubs or Chalicodomae in the perfect state

who have died without being able to effect their deliverance.



Should all the rooms be available, a rare occurrence, there still

remains a method of distinguishing between an ancient nest and a

recent one. The cocoon, as I have said, adheres pretty closely to the

walls; and the mother does not always take away this remnant, either

because she is unable to do so, or because she considers the removal

unnecessary. Thus the base of the new cocoon is set in the bottom of

the old cocoon. This double wrapper points very clearly to two

generations, two separate years. I have even found as many as three

cocoons fitting one into another at their bases. Consequently, the

nests of the Mason-bee of the Pebbles are able to do duty for three

years, if not more. Eventually they become utter ruins, abandoned to

the Spiders and to various smaller Bees or Wasps, who take up their

quarters in the crumbling rooms.



As we see, an old nest is hardly ever capable of containing the

Mason-bee's entire laying, which calls for some fifteen apartments.

The number of rooms at her disposal is most unequal, but always very

small. It is saying much when there are enough to receive about half

the laying. Four or five cells, sometimes two or even one: that is

what the Mason usually finds in a nest that is not her own work. This

large reduction is explained when we remember the numerous parasites

that live upon the unfortunate Bee.



Now, how are the sexes distributed in those layings which are

necessarily broken up between one old nest and another? They are

distributed in such a way as utterly to upset the idea of an

invariable succession first of females and then of males, the idea

which occurs to us on examining the new nests. If this rule were a

constant one, we should be bound to find in the old domes at one time

only females, at another only males, according as the laying was at

its first or at its second stage. The simultaneous presence of the

two sexes would then correspond with the transition period between

one stage and the next and should be very unusual. On the contrary,

it is very common; and, however few cells there may be, we always

find both females and males in the old nests, on the sole condition

that the compartments have the regulation holding-capacity, a large

capacity for the females, a lesser for the males, as we have seen.



The old male cells can be recognized by their position on the outer

edges and by their capacity, measuring on an average the same as a

column of sand 31 millimetres high in a glass tube 5 millimetres

wide. (1.21 x .195 inches.--Translator's Note.) These cells contain

males of the second or third generation and none but males. In the

old female cells, those in the middle, whose capacity is measured by

a similar column of sand 45 millimetres high (1.75 inches.--

Translator's Note.), are females and none but females.



This presence of both sexes at a time, even when there are but two

cells free, one spacious and the other small, proves in the plainest

fashion that the regular distribution observed in the complete nests

of recent production is here replaced by an irregular distribution,

harmonizing with the number and holding-capacity of the chambers to

be stocked. The Mason-bee has before her, let me suppose, only five

vacant cells: two larger and three smaller. The total space at her

disposal would do for about a third of the laying. Well, in the two

large cells, she puts females; in the three small cells, she puts

males.



As we find the same sort of thing in all the old nests, we must needs

admit that the mother knows the sex of the egg which she is going to

lay, because that egg is placed in a cell of the proper capacity. We

can go further and admit that the mother alters the order of

succession of the sexes at her pleasure, because her layings, between

one old nest and another, are broken up into small groups of males

and females according to the exigencies of space in the actual nest

which she happens to be occupying.



Just now, in the new nest, we saw the Mason-bee arranging her total

laying into series first of females and next of males; and here she

is, mistress of an old nest of which she has not the power to alter

the arrangement, breaking up her laying into sections comprising both

sexes just as required by the conditions imposed upon her. She

therefore decides the sex of the egg at will, for, without this

prerogative, she could not, in the chambers of the nest which she

owes to chance, deposit unerringly the sex for which those chambers

were originally built; and this happens however small the number of

chambers to be filled.



When the nest is new, I think I see a reason why the Mason-bee should

seriate her laying into females and then males. Her nest is a half-

sphere. That of the Mason-bee of the Shrubs is very nearly a sphere.

Of all shapes, the spherical shape is the strongest. Now these two

nests require an exceptional power of resistance. Without protection

of any kind, they have to brave the weather, one on its pebble, the

other on its bough. Their spherical configuration is therefore very

practical.



The nest of the Mason-bee of the Walls consists of a cluster of

upright cells backing against one another. For the whole to take a

spherical form, the height of the chambers must diminish from the

centre of the dome to the circumference. Their elevation is the sine

of the meridian arc starting from the plane of the pebble. Therefore,

if they are to have any solidity, there must be large cells in the

middle and small cells at the edges. And, as the work begins with the

central chambers and ends with those on the circumference, the laying

of the females, destined for the large cells, must precede that of

the males, destined for the small cells. So the females come first

and the males at the finish.



This is all very well when the mother herself founds the dwelling,

when she lays the first rows of bricks. But, when she is in the

presence of an old nest, of which she is quite unable to alter the

general arrangement, how is she to make use of the few vacant rooms,

the large and the small alike, if the sex of the egg be already

irrevocably fixed? She can only do so by abandoning the arrangement

in two consecutive rows and accommodating her laying to the varied

exigencies of the home. Either she finds it impossible to make an

economical use of the old nest, a theory refuted by the evidence, or

else she determines at will the sex of the egg which she is about to

lay.



The Osmiae themselves will furnish the most conclusive evidence on

the latter point. We have seen that these Bees are not generally

miners, who themselves dig out the foundation of their cells. They

make use of the old structures of others, or else of natural

retreats, such as hollow stems, the spirals of empty shells and

various hiding-places in walls, clay or wood. Their work is confined

to repairs to the house, such as partitions and covers. There are

plenty of these retreats; and the insect would always find first-

class ones if it thought of going any distance to look for them. But

the Osmia is a stay-at-home: she returns to her birth-place and

clings to it with a patience extremely difficult to exhaust. It is

here, in this little familiar corner, that she prefers to settle her

progeny. But then the apartments are few in number and of all shapes

and sizes. There are long and short ones, spacious ones and narrow.

Short of expatriating herself, a Spartan course, she has to use them

all, from first to last, for she has no choice. Guided by these

considerations, I embarked on the experiments which I will now

describe.



I have said how my study, on two separate occasions, became a

populous hive, in which the Three-horned Osmia built her nests in the

various appliances which I had prepared for her. Among these

appliances, tubes, either of glass or reed, predominated. There were

tubes of all lengths and widths. In the long tubes, entire or almost

entire layings, with a series of females followed by a series of

males, were deposited. As I have already referred to this result, I

will not discuss it again. The short tubes were sufficiently varied

in length to lodge one or other portion of the total laying. Basing

my calculations on the respective lengths of the cocoons of the two

sexes, on the thickness of the partitions and the final lid, I

shortened some of these to the exact dimensions required for two

cocoons only, of different sexes.



Well, these short tubes, whether of glass or reed, were seized upon

as eagerly as the long tubes. Moreover, they yielded this splendid

result: their contents, only a part of the total laying, always began

with female and ended with male cocoons. This order was invariable;

what varied was the number of cells in the long tubes and the

proportion between the two sorts of cocoons, sometimes males

predominating and sometimes females.



The experiment is of paramount importance; and it will perhaps make

the result clearer if I quote one instance from among a multitude of

similar cases. I give the preference to this particular instance

because of the rather exceptional fertility of the laying. An Osmia

marked on the thorax is watched, day by day, from the commencement to

the end of her work. From the 1st to the 10th of May, she occupies a

glass tube in which she lodges seven females followed by a male,

which ends the series. From the 10th to the 17th of May, she

colonizes a second tube, in which she lodges first three females and

then three males. From the 17th to the 25th of May, a third tube,

with three females and then two males. On the 26th of May, a fourth

tube, which she abandons, probably because of its excessive width,

after laying one female in it. Lastly, from the 26th to the 30th of

May, a fifth tube, which she colonizes with two females and three

males. Total: twenty-five Osmiae, including seventeen females and

eight males. And it will not be superfluous to observe that these

unfinished series do not in any way correspond with periods separated

by intervals of rest. The laying is continuous, in so far as the

variable condition of the atmosphere allows. As soon as one tube is

full and closed, another is occupied by the Osmia without delay.



The tubes reduced to the exact length of two cells fulfilled my

expectation in the great majority of cases: the lower cell was

occupied by a female and the upper by a male. There were a few

exceptions. More discerning than I in her estimate of what was

strictly necessary, better-versed in the economy of space, the Osmia

had found a way of lodging two females where I had only seen room for

one female and a male.



This experiment speaks volumes. When confronted with tubes too small

to receive all her family, she is in the same plight as the Mason-bee

in the presence of an old nest. She thereupon acts exactly as the

Chalicodoma does. She breaks up her laying, divides it into series as

short as the room at her disposal demands; and each series begins

with females and ends with males. This breaking up, on the one hand,

into sections in all of which both sexes are represented and the

division, on the other hand, of the entire laying into just two

groups, one female, the other male, when the length of the tube

permits, surely provide us with ample evidence of the insect's power

to regulate the sex of the egg according to the exigencies of space.



And besides the exigencies of space one might perhaps venture to add

those connected with the earlier development of the males. These

burst their cocoons a couple of weeks or more before the females;

they are the first who hasten to the sweets of the almond-tree. In

order to release themselves and emerge into the glad sunlight without

disturbing the string of cocoons wherein their sisters are still

sleeping, they must occupy the upper end of the row; and this, no

doubt, is the reason that makes the Osmia end each of her broken

layings with males. Being next to the door, these impatient ones will

leave the home without upsetting the shells that are slower in

hatching.



I experimented on Latreille's Osmia, using short and even very short

stumps of reed. All that I had to do was to lay them just beside the

nests of the Mason-bee of the Sheds, nests beloved by this particular

Osmia. Old, disused hurdles supplied me with reeds inhabited from end

to end by the Horned Osmia. In both cases I obtained the same results

and the same conclusions as with the Three-horned Osmia.



I return to the latter, nidifying under my eyes in some old nests of

the Mason-bee of the Walls, which I had placed within her reach,

mixed up with the tubes. Outside my study, I had never yet seen the

Three-horned Osmia adopt that domicile. This may be due to the fact

that these nests are isolated one by one in the fields; and the

Osmia, who loves to feel herself surrounded by her kin and to work in

plenty of company, refuses them because of this isolation. But on my

table, finding them close to the tubes in which the others are

working, she adopts them without hesitation.



The chambers presented by those old nests are more or less spacious

according to the thickness of the coat of mortar which the

Chalicodoma has laid over the assembled chambers. To leave her cell,

the Mason-bee has to perforate not only the plug, the lid built at

the mouth of the cell, but also the thick plaster wherewith the dome

is strengthened at the end of the work. The perforation results in a

vestibule which gives access to the chamber itself. It is this

vestibule which is sometimes longer and sometimes shorter, whereas

the corresponding chamber is of almost constant dimensions, in the

case of the same sex, of course.



We will first consider the short vestibule, at the most large enough

to receive the plug with which the Osmia will close up the lodging.

There is then nothing at her disposal except the cell proper, a

spacious apartment in which one of the Osmia's females will find

ample accommodation, for she is much smaller than the original

occupant of the chamber, no matter the sex; but there is not room for

two cocoons at a time, especially in view of the space taken up by

the intervening partition. Well, in those large, well-built chambers,

formerly the homes of Chalicodomae, the Osmia settles females and

none but females.



Let us now consider the long vestibule. Here, a partition is

constructed, encroaching slightly on the cell proper, and the

residence is divided into two unequal storeys, a large room below,

housing a female, and a narrow cabin above, containing a male.



When the length of the vestibule permits, allowing for the space

required by the outer stopper, a third storey is built, smaller than

the second; and another male is lodged in this cramped corner. In

this way the old nest of the Mason-bee of the Pebbles is colonized,

cell after cell, by a single mother.



The Osmia, as we see, is very frugal of the lodging that has fallen

to her share; she makes the best possible use of it, giving to the

females the spacious chambers of the Mason-bee and to the males the

narrow vestibules, subdivided into storeys when this is feasible.

Economy of space is the chief consideration, since her stay-at-home

tastes do not allow her to indulge in distant quests. She has to

employ the site which chance places at her disposal just as it is,

now for a male and now for a female. Here we see displayed, more

clearly than ever, her power of deciding the sex of the egg, in order

to adapt it judiciously to the conditions of the house-room

available.



I had offered at the same time to the Osmiae in my study some old

nests of the Mason-bee of the Shrubs, which are clay spheroids with

cylindrical cavities in them. These cavities are formed, as in the

old nests of the Mason-bee of the Pebbles, of the cell properly so-

called and of the exit-way which the perfect insect cut through the

outer coating at the time of its deliverance. Their diameter is about

seven millimetres (.273 inch.--Translator's Note.); their depth at

the centre of the heap is 23 millimetres (.897 inch.--Translator's

Note.); and at the edge averages 14 millimetres (.546 inch.--

Translator's Note.)



The deep central cells receive only the females of the Osmia;

sometimes even the two sexes together, with a partition in the

middle, the female occupying the lower and the male the upper storey.

True, in such cases economy of space is strained to the utmost, the

apartments provided by the Mason-bee of the Shrubs being very small

as it is, despite their entrance-halls. Lastly, the deeper cavities

on the circumference are allotted to females and the shallower to

males.



I will add that a single mother peoples each nest and also that she

proceeds from cell to cell without troubling to ascertain the depth.

She goes from the centre to the edges, from the edges to the centre,

from a deep cavity to a shallow cavity and vice versa, which she

would not do if the sexes were to follow upon each other in a settled

order. For greater certainty, I numbered the cells of one nest as

each of them was closed. On opening them later, I was able to see

that the sexes were not subjected to a chronological arrangement.

Females were succeeded by males and these by females without its

being possible for me to make out any regular sequence. Only--and

this is the essential point--the deep cavities were allotted to the

females and the shallow ones to the males.



We know that the Three-horned Osmia prefers to haunt the habitations

of the Bees who nidify in populous colonies, such as the Mason-bee of

the Sheds and the Hairy-footed Anthophora. Exercising the very

greatest care, I broke up some great lumps of earth removed from the

banks inhabited by the Anthophora and sent to me from Carpentras by

my dear friend and pupil M. Devillario. I examined them

conscientiously in the quiet of my study. I found the Osmia's cocoons

arranged in short series, in very irregular passages, the original

work of which is due to the Anthophora. Touched up afterwards, made

larger or smaller, lengthened or shortened, intersected with a

network of crossings by the numerous generations that had succeeded

one another in the same city, they formed an inextricable labyrinth.



Sometimes these corridors did not communicate with any adjoining

apartment; sometimes they gave access to the spacious chamber of the

Anthophora, which could be recognized, in spite of its age, by its

oval shape and its coating of glazed stucco. In the latter case, the

bottom cell, which once constituted, by itself, the chamber of the

Anthophora, was always occupied by a female Osmia. Beyond it, in the

narrow corridor, a male was lodged, not seldom two, or even three. Of

course, clay partitions, the work of the Osmia, separated the

different inhabitants, each of whom had his own storey, his own

closed cell.



When the accommodation consisted of no more than a simple cylinder,

with no state-bedroom at the end of it--a bedroom always reserved for

a female--the contents varied with the diameter of the cylinder. The

series, of which the longest were series of four, included, with a

wider diameter, first one or two females, then one or two males. It

also happened, though rarely, that the series was reversed, that is

to say, it began with males and ended with females. Lastly, there

were a good many isolated cocoons, of one sex or the other. When the

cocoon was alone and occupied the Anthophora's cell, it invariably

belonged to a female.



I have observed the same thing in the nests of the Mason-bee of the

Sheds, but not so easily. The series are shorter here, because the

Mason-bee does not bore galleries but builds cell upon cell. The work

of the whole swarm thus forms a stratum of cells that grows thicker

from year to year. The corridors occupied by the Osmia are the holes

which the Mason-bee dug in order to reach daylight from the deep

layers. In these short series, both sexes are usually present; and,

if the Mason-bee's chamber is at the end of the passage, it is

inhabited by a female Osmia.



We come back to what the short tubes and the old nests of the Mason-

bee of the Pebbles have already taught us. The Osmia who, in tubes of

sufficient length, divides her whole laying into a continuous

sequence of females and a continuous sequence of males, now breaks it

up into short series in which both sexes are present. She adapts her

sectional layings to the exigencies of a chance lodging; she always

places a female in the sumptuous chamber which the Mason-bee or the

Anthophora occupied originally.



Facts even more striking are supplied by the old nests of the Masked

Anthophora (A. personata, ILLIG.), old nests which I have seen

utilized by the Horned Osmia and the Three-horned Osmia at the same

time. Less frequently, the same nests serve for Latreille's Osmia.

Let us first describe the Masked Anthophora's nests.



In a steep bank of sandy clay, we find a set of round, wide-open

holes. There are generally only a few of them, each about half an

inch in diameter. They are the entrance-doors leading to the

Anthophora's abode, doors always left open, even after the building

is finished. Each of them gives access to a short passage, sometimes

straight, sometimes winding, nearly horizontal, polished with minute

care and varnished with a sort of white glaze. It looks as if it had

received a thin coat of whitewash. On the inner surface of this

passage, in the thickness of the earthy bank, spacious oval niches

have been excavated, communicating with the corridor by means of a

narrow bottle-neck, which is closed, when the work is done, with a

substantial mortar stopper. The Anthophora polishes the outside of

this stopper so well, smooths its surface so perfectly, bringing it

to the same level as that of the passage, is so careful to give it

the white tint of the rest of the wall that, when the job is

finished, it becomes absolutely impossible to distinguish the

entrance-door corresponding with each cell.



The cell is an oval cavity dug in the earthy mass. The wall has the

same polish, the same chalky whiteness as the general passage. But

the Anthophora does not limit herself to digging oval niches: to make

her work more solid, she pours over the walls of the chamber a

salivary liquid which not only whitens and varnishes but also

penetrates to a depth of some millimetres into the sandy earth, which

it turns into a hard cement. A similar precaution is taken with the

passage; and therefore the whole is a solid piece of work capable of

remaining in excellent condition for years.



Moreover, thanks to the wall hardened by the salivary fluid, the

structure can be removed from its matrix by chipping it carefully

away. We thus obtain, at least in fragments, a serpentine tube from

which hangs a single or double row of oval nodules that look like

large grapes drawn out lengthwise. Each of these nodules is a cell,

the entrance to which, carefully hidden, opens into the tube or

passage. When she wishes to leave her cell, in the spring, the

Anthophora destroys the mortar disk that closes the jar and thus

reaches the general corridor, which is quite open to the outer air.

The abandoned nest provides a series of pear-shaped cavities, of

which the distended part is the old cell and the contracted part the

exit-neck, rid of its stopper.



These pear-shaped hollows form splendid lodgings, impregnable

strongholds, in which the Osmiae find a safe and commodious retreat

for their families. The Horned Osmia and the Three-horned Osmia

establish themselves there at the same time. Although it is a little

too large for her, Latrielle's Osmia also appears very well satisfied

with it.



I have examined some forty of the superb cells utilized by each of

the first two. The great majority are divided into two storeys by

means of a transversal partition. The lower storey includes the

larger portion of the Anthophora's cell; the upper storey includes

the rest of the cell and a little of the bottle-neck that surmounts

it. The two-roomed dwelling is closed, in the passage, by a

shapeless, bulky mass of dried mud. What a clumsy artist the Osmia

is, compared with the Anthophora! Against the exquisite work of the

Anthophora, partition and plug strike a note as hideously incongruous

as a lump of dirt on polished marble.



The two apartments thus obtained are of a very unequal capacity,

which at once strikes the observer. I measured them with my five-

millimetre tube. On an average, the bottom one is represented by a

column of sand 50 millimetres deep (1.95 inches.--Translator's Note.)

and the top one by a column of 15 millimetres (.585 inch.--

Translator's Note.). The holding-capacity of the one is therefore

about three times as large as that of the other. The cocoons enclosed

present the same disparity. The bottom one is big, the top one small.

Lastly, the lower one belongs to a female Osmia and the upper to a

male Osmia.



Occasionally the length of the bottle-neck allows of a fresh

arrangement and the cavity is divided into three storeys. The bottom

one, which is always the most spacious, contains a female; the two

above, both smaller than the first and one smaller than the other,

contain males.



Let us keep to the first case, which is always the most frequent. The

Osmia is in the presence of one of these pear-shaped hollows. It is a

find that must be employed to the best advantage: a prize of this

sort is rare and falls only to fortune's favourites. To lodge two

females in it at once is impossible; there is not sufficient room. To

lodge two males in it would be undue generosity to a sex that is

entitled to but the smallest consideration. Besides, the two sexes

must be represented in almost equal numbers. The Osmia decides upon

one female, whose portion shall be the better room, the lower one,

which is larger, better-protected and more nicely polished, and one

male, whose portion shall be the upper storey, a cramped attic,

uneven and rugged in the part which encroaches on the bottle-neck.

This decision is proved by numerous undeniable facts. Both Osmiae

therefore can choose the sex of the egg about to be laid, seeing that

they are now breaking up the laying into groups of two, a female and

a male, as required by the conditions of the lodging.



I have only once found Latreille's Osmia established in the nest of

the Masked Anthophora. She had occupied but a small number of cells,

because the others were not free, being inhabited by the Anthophora.

The cells in question were divided into three storeys by partitions

of green mortar; the lower storey was occupied by a female, the two

others by males, with smaller cocoons.



I came to an even more remarkable example. Two Anthidia of my

district, A. septemdentatum, LATR., and A. bellicosum, LEP., adopt as

the home of their offspring the empty shells of different snails:

Helix aspersa, H. algira, H. nemoralis, H. caespitum. The first-

named, the Common Snail, is the most often used, under the stone-

heaps and in the crevices of old walls. Both Anthidia colonize only

the second whorl of the spiral. The central part is too small and

remains unoccupied. Even so with the front whorl, the largest, which

is left completely empty, so much so that, on looking through the

opening, it is impossible to tell whether the shell does or does not

contain the Bee's nest. We have to break this last whorl if we would

perceive the curious nest tucked away in the spiral.



We then find first a transversal partition, formed of tiny bits of

gravel cemented by a putty made from resin, which is collected in

fresh drops from the oxycedrus and the Aleppo pine. Beyond this is a

stout barricade made up of rubbish of all kinds: bits of gravel,

scraps of earth, juniper-needles, the catkins of the conifers, small

shells, dried excretions of Snails. Next come a partition of pure

resin, a large cocoon in a roomy chamber, a second partition of pure

resin and, lastly, a smaller cocoon in a narrow chamber. The

inequality of the two cells is the necessary consequence of the shape

of the shell, whose inner space gains rapidly in width as the spiral

gets nearer to the orifice. Thus, by the mere general arrangement of

the home and without any work on the Bee's part beyond some slender

partitions, a large room is marked out in front and a much smaller

room at the back.



By a very remarkable exception, which I have mentioned casually

elsewhere, the males of the genus Anthidium are generally larger than

the females; and this is the case with the two species in particular

that divide the Snail's spiral with resin partitions. I collected

some dozens of nests of both species. In at least half the cases, the

two sexes were present together; the female, the smaller, occupied

the front cell and the male, the bigger, the back cell. Other cells,

which were smaller or too much obstructed at the back by the dried-up

remains of the Mollusc, contained only one cell, occupied at one time

by a female and at another by a male. A few, lastly, had both cells

inhabited now by two males and now by two females. The most frequent

arrangement was the simultaneous presence of both sexes, with the

female in front and the male behind. The Anthidia who make resin-

dough and live in Snail-shells can therefore alternate the sexes

regularly to meet the exigencies of the spiral dwelling-house.



One more thing and I have done. My apparatus of reeds, fixed against

the walls of the garden, supplied me with a remarkable nest of the

Horned Osmia. The nest is established in a bit of reed 11 millimetres

wide inside. (.429 inch--Translator's Note.) It comprises thirteen

cells and occupies only half the cylinder, although the orifice is

plugged with the usual stopper. The laying therefore seems here to be

complete.



Well, this laying is arranged in a most singular fashion. There is

first, at a suitable distance from the bottom or the node of the

reed, a transversal partition, perpendicular to the axis of the tube.

This marks off a cell of unusual size, in which a female is lodged.

After that, in view of the excessive width of the tunnel, which is

too great for a series in single file, the Osmia appears to alter her

mind. She therefore builds a partition perpendicular to the

transversal partition which she has just constructed and thus divides

the second storey into two rooms, a larger room, in which she lodges

a female, and a smaller, in which she lodges a male. She next builds

a second transversal partition and a second longitudinal partition

perpendicular to it. These once more give two unequal chambers,

stocked likewise, the large one with a female, the smaller one with a

male.



>From this third storey onwards, the Osmia abandons geometrical

accuracy; the architect seems to be a little out in her reckoning.

The transversal partitions become more and more slanting and the work

grows irregular, but always with a sprinkling of large chambers for

the females and small chambers for the males. Three females and two

males are housed in this way, the sexes alternating.



By the time that the base of the eleventh cell is reached, the

transversal partition is once more almost perpendicular to the axis.

Here what happened at the bottom is repeated. There is no

longitudinal partition; and the spacious cell, covering the whole

diameter of the cylinder, receives a female. The edifice ends with

two transversal partitions and one longitudinal partition, which mark

out, on the same level, chambers twelve and thirteen, both of which

contain males.



There is nothing more curious than this mixing of the two sexes, when

we know with what precision the Osmia separates them in a linear

series, where the narrow width of the cylinder demands that the cells

shall be set singly, one above the other. Here, the Bee is making use

of a tube whose diameter is not suited to her work; she is

constructing a complex and difficult edifice, which perhaps would not

possess the necessary solidity if the ceilings were too broad. The

Osmia therefore supports these ceilings with longitudinal partitions;

and the unequal chambers resulting from the introduction of these

partitions receive females at one time and males at another,

according to their capacity.





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