Page:Popular Science Monthly Volume 3.djvu/682

664 that live upon other leaves than the mulberry. Among these new importations, the two principal ones are the yama-maï worm, which comes from Japan, and feeds upon the leaves of the oak, and the ailanthus worm. The first gives a very beautiful and very fine silk, while that of the second is dull and coarse. But the ailanthus grows very well in unproductive soils, and hence the caterpillar which it nourishes renders an important service.

But let us return to our mulberry caterpillar, or the silk-worm properly so called. We left it at the moment when it disappeared from our eyes enveloped in its cocoon. There, in its mysterious retreat, it becomes torpid once more. It now shortens itself, changes form, and submits to a fifth moulting. But the animal which emerges from the old skin is no longer a caterpillar. It is in some sort a new being; it is what we call a chrysalis. This chrysalis scarcely reminds us of the silk-worm. The body is entirely swaddled; we no longer see either head or feet (Fig. 14). The color is changed, and has become a golden yellow. Only by certain obscure movements of the posterior part do we know that it is not a dead body.

This apparent torpor in reality conceals a strange activity in all the organs and all the tissues, which ends in the transformation of the entire being.

In fifteen or seventeen days, according to the temperature, this work is accomplished, and the last crisis arrives. The skin splits on the back; the animal moults for the last time, but the creature that now appears is no longer a caterpillar or a chrysalis: it is a butterfly (Fig. 12).



Is it needful to explain the details of this wonderful metamorphosis? The body, before almost all alike, presents now three distinct regions: the head, the chest (thorax), the belly (abdomen). Wings, of which there was not the least vestige, are now developed. In compensation, the hind-feet have disappeared. The fore-feet persist, but you would not know them, they have become so slender, and a fine down covers all the parts.

In the interior, the transformation is also complete. The œsophagus (throat) is no longer a simple reversed funnel; it is a narrow, lengthened tube, with an aerial vessel attached, of which the caterpillar offers no trace. The stomach is strangely shortened. The