anthophora emerge from the pupæ sooner than the females, and M. Fabre ascertained that, as they come out of their galleries, the little sitaris larvæ fasten upon them. Not, however, for long: instinct teaches them that they are not yet in the straight path of development; and, watching their opportunity, they pass from the male to the female bee. Guided by these indications, M. Fabre examined several cells of anthophora ; in some, the egg of the anthophora floated by itself on the surface of the honey: in others, on the egg, as on a raft, sat the still more minute larva of the sitaris. The mystery was solved. At the moment when the egg is laid, the sitaris larva springs upon it. Even while the poor mother is carefully fastening up her cell, her mortal enemy is beginning to devour her offspring; for the egg of the anthophora serves not only as a raft, but as a repast. The honey, which is enough for either, would be too little for both; and the sitaris, therefore, at its first meal, relieves itself from its only rival. After eight days the egg is consumed, and on the empty shell the sitaris undergoes its first transformation, and makes its appearance in a very different form.

The honey, which was fatal before, is now necessary, the activity, which before was necessary, is now useless consequently, with the change of skin, the active, slim larva changes into a white, fleshy grub, so organized as to float on the surface of the honey, with the mouth beneath and the spiracles above the surface: "Grâce à l'embonpoint du ventre," says M. Fabre, "la larve est à l'abri de l'asphyxie." In this state it remains until the honey is consumed; then the animal contracts, and detaches itself from its skin, within which the further

transformations take place. In the next stage, which M. Fabre calls the pseudo-chrysalis, the larva has a solid corneous envelope and an oval shape, and in its colour, consistency, and immobility, reminds one of a dipterous pupa. The time passed in this condition varies much. When it has elapsed, the animal moults again, again changes its form; after this it becomes a pupa, without any remarkable peculiarities. Finally, after these wonderful changes and adventures, in the month of August the perfect beetle makes its appearance.

In fact, whenever in any group we find differences in form or colour, we shall always find them associated with differences in habit. Let us take the case of caterpillars. The prevailing colour of caterpillars is green, like that of leaves. The value of this to the young insect, the protection it affords, are obvious. We must all have observed how difficult it is to distinguish small green caterpillars from the leaves on which they feed. When, however, they become somewhat larger, their form betrays them, and it is important that there should be certain marks to divert the eye from the outlines of the body. This is effected, and much protection given, by longitudinal lines (Fig. 38), which accordingly are found on a great many caterpillars. These lines, both in colour and thickness, much resemble some of the lines on leaves (especially those, for instance, of grasses), and also the streaks of shadow which occur among foliage. If, however, this be the explanation of them, then they ought to be wanting, as a general rule, in very small caterpillars, and to prevail most among those which feed on or among grasses. Now, similar lines occur on a great number of caterpillars belonging to most different groups

of butterflies and moths, as you may see by turning over the illustrations of any monograph of the group. They exist among the hawk-moths, as, for instance, in the humming-bird hawk-moth; they occur in many butterflies, as, in Arge galathea, which feeds on the cat's-tail grass; and in many moths, as, for instance, in Pyrophila tragopoginis, which feeds on the leaves

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FIG. 38.-Arge galathea.

of the "John Go-to-bed at Noon" (Tragopogon). But you will find that the smallest caterpillars rarely possess these white streaks. As regards the second point also, the streaks are generally wanting in caterpillars which feed on large-leaved plants. The Satyrida, on the contrary, all possess them, and all live on grass. In fact we may say, as a general rule, that these longi

tudinal streaks only occur on caterpillars which live on or among narrow-leaved plants. As the insect grows, these lines often disappear on certain segments, and are replaced by diagonal lines. These diagonal lines (Fig. 39) occur in a great many caterpillars, belonging to the most distinct families of butterflies and moths. They come off just at the same angle as the ribs of leaves, and resemble them very much in general effect. They occur also especially in species which fecd on large-leaved plants, and I believe I may say that though a great many species of caterpillars present these lines, they

rarely, if ever, occur in species which live on grass; while, on the contrary, they are very frequent in those species which live on large-leaved plants. It might at first be objected to this view that there are many cases, as in the elephant hawk-moth, in which caterpillars have both. A little consideration, however, will explain this. In small caterpillars these oblique lines would be useless, because they must have some relation, not only in colour, but in their distance apart, to the ribs of the leaves. Hence, while there are a great many species which have longitudinal lines when young, and diagonal ones when they are older and larger, there is not, I believe, a single

cuous.

one which begins with diagonal lines, and then replaces them with longitudinal ones. The disappearance of the longitudinal lines on those segments which have diagonal ones, is striking, where the lines are marked. It is an advantage, because white lines crossing one another at such an angle have no relation to anything which occurs in plants, and would make the creature more conspiWhen, therefore, the diagonal lines are developed, the longitudinal ones often disappear. There is one other point in connection with these diagonal lines to which I must call your attention. In many species they are white, but in some cases, as for instance in the beautiful green caterpillar of the privet hawk-moth, the white streak is accompanied by a coloured one-in that case lilac. At first we might think that this would be a disadvantage, as tending to make the caterpillar more conspicuous; and in fact, if we put one in full view, for instance, out on a table, and focus the eye on it, the coloured lines are very striking. But we must remember that the habit of the insect is to sit on the lower side of the leaf, generally near the midrib, and in the subdued light of such a situation, especially if the eye be not looking exactly at them, the coloured lines beautifully simulate a line of soft shadow, such as must always accompany a strong rib; and I need not tell any artist that the shadows of yellowish green must be purplish. Moreover, any one who has ever found one of these large caterpillars will, I am sure, agree with me that it is surprising, when we consider their size and conspicuous colouring, how difficult they are to see. But though the prevailing colour of caterpillars is green, there are numerous exceptions. In one great

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