equal length. Besides these, we find the lower end of the bowel, containing all the undigested food and excretions which have accumulated there since the larva first began to feed. The reason of this singular arrangement will be obvious on a little consideration. Placed as the larva is, vertically, in a closely fitting cell, which it cannot leave, and from which there could be no drainage except by the side of its body, it is necessary to provide against this contingency, and also against the decomposition of the excreted matters. The object is effected, as usual, in the simplest possible way: the excreta are retained not only within a membrane, but within the body of the larva, secured, as far as may be, from chemical influences, and from becoming a source of injury to the helpless larva. Thus :-in the larva of the wasp the bowel does not open by a vent externally, but terminates in a blind pouch, which receives all the excretions and the undigested residue of the food. The smallest atom of a larva has often a dark speck visible through its skin. This grows larger, with the growth of the larva, till the second moulting, when it is cast off with the skin, as a hard black mass closely invested with the membrane which formed the end of the bowel. On examination with the microscope, this mass is found to consist of scales, hairs, and other fragments of insects, hairs of vegetables, and other substances less easy of recognition. From this inventory it would seem that, from the earliest period of their existence, these little mites are fed on chopped insects. An observation of Wildman confirms this inference, and shows that the mandibles of the larvæ are meant for real work, to

chop their food smaller still. For he has seen the adult wasps supplying the larvæ with masses of solid food of such a size as to require to be cut up into smaller pieces before they could be swallowed.* If the benefit of insects to man is to be measured by the number of other insects that they destroy, wasps must be our benefactors indeed.

When the perfect insect leaves its cell it leaves its prison history written on the walls in very plain characters. Here is the egg-shell, wanting only a little patience to spread it out in its full proportions. Here, close by, is the first skin, at once distinguished by the great length of the central tooth of the mandibles. Pressed down upon these relics of an earlier age, earlier by a fortnight perhaps, is the spiral coil of undigested food wrapped in its own membranes, a daily record of all that the little grub has eaten, or rather has failed to digest. On this lies the second skin and its mandibles, needing a great deal of patience to disentangle it perfectly; and on this, again, we may find as much of the cast skin of the pupa as has not been either swallowed by the insect just emerging into active life, or picked out of the deserted cell piecemeal by her elder sisters. And this story is repeated, in the same way, as many times as the cell has been occupied; egg-shell, first skin, excreted mass, second skin, and shreds of pupal investment lie in sets, in the same order as they have been cast off by each successive tenant.

There has long been a discrepancy of opinion

* Wildman, 'A Treatise on the Management of Bees,' &c. 4to. London, 1768, p. 158, "so large that they were scarce able to swallow "them."

among Naturalists as to the changes which the beelarva undergoes, and the number of times that it casts its skin. The interest which attaches to the subject on this account, and the light which the history of the bee and wasp mutually throw on each other must be my excuse for a somewhat long digression into the history of the larva of the honeybee. This inquiry is altogether much more difficult than the examination of the wasp-larva. For the structures are much slighter; they are not to be displayed without a great deal of trouble, and, after all, there is much less to see. With a saucer of warm water we can loosen and unravel all the parts of a wasp's comb, but the honey-comb requires long soaking in an alkaline solution to separate the silk lining from the waxen wall. Under this treatment, however, the cocoons will float out entire, and incidentally we may satisfy ourselves of a fact which has been often disputed, namely that cells which have not been used for breeding, but only for storing honey in, have no lining. Indeed, as the lining of the cell is the cocoon of the larva, it could not be otherwise.

As the bee-larva is fed on bee-bread, which leaves little or no indigestible residue, the grub is not provided with a large pouch within its body to receive such matters. The yellow substance which we find in the angles of the bottom of the bee-cell is shown by the microscope to consist almost entirely of pollen granules, and to be, in fact, identical with bee-bread. It is probably superabundant food which the larva has not eaten, and which has worked its way down to the bottom of the cell. It certainly is

not the undigested residue of food, for it lies outside the cocoon, and must therefore have been deposited there before the larva had begun to weave this, and had cast its second skin, before therefore the bowel of the larva has become pervious. Besides, the deposit lies loose, not enveloped in a membrane, as the contents of the intestines of the larva would have been. The absence of uric acid supplies another-however slight-argument in favour of the conclusion that this deposit never passed through the intestines. It is very small in quantity compared with the dark mass which encroaches so sensibly on the depth of the wasps' cell.

The thickest part of the cocoon of the wasp is at the cap, in connection probably with the fact that the faculty of making silk continues to be an attribute of the perfect wasp, while the bee only makes silk this once in her life. On the contrary, the bottom of the bee's cocoon is the thickest part of her flimsy structure. Held in shape by the adherent pollen granules, it seems to be thicker than it really is in this place. As the bee-larva grows its power of making silk gradually fails, and the cap of the cocoon is so thin that the workers have to make good the deficiency by plastering this end over with wax. Otherwise the pupa would be dried up within her case. It is curious to notice how one thing compensates for another; the wax cell-walls, and the elder sisters at hand to stop the pervious end of the cocoon with wax, make up for the slightness and deficiencies of the work of the larva.

The number of the successive tenants of a bee'scell may be most easily counted at the bottom, where

the cocoons are thickest. Hunter* has reckoned as many as twenty separate linings, which, though they occupied little space when dry, swelled up when moistened with water so as to rise to the mouth of the cell. From the fact of the sac being quite closed at the bottom it is clear that the cocoon is commenced at a time when the small size of the larva allowed her to move about freely in the cell. But even then the lining could scarcely have been made so complete if the cell had not been placed horizontally, instead of vertically like the wasp's. A wasplarva has to hold tightly to the wall of her cell all the time she is spinning, to prevent her falling out. But the connection of the bee-larva to the cell is altogether less firm than that of the wasp. Huntert often found that the eggs and larvæ of his bees had been removed by the swarm from one cell to another. The inventory of the bee's cell after the insect has flown seems at first sight very scanty, compared with that of the wasp. However, if we look close, we shall find everything there. Draw one cocoon very carefully away from another, and examine its rough end, outside, under water of course. On the yellow matter we shall find a whitish tuft, quite distinct in appearance from the cocoon membrane, which, from the fragments of tissues which it bears. about it, is evidently a cast skin. Often a smaller and less composite membrane breaks away from this, which I believe, after careful examination, to be the egg-shell.

This is just the same as we have seen in the wasp,

* Hunter. 'Observations on Bees.' Works. Vol. IV. p. 466. + Op. cit. p. 440.