and a hook still more enlarged.
(After Sharp.)
As almost all the chrysalids here considered are figured in the illustrations, it will be unnecessary to refer in detail to their great diversity in form, but a few general remarks on the structure of a chrysalis may be made.
If the upper (dorsal) surface of a chrysalis is examined, the thorax and the body divisions will easily be made out, while, by looking at the sides and the under (ventral) surface, the various organs, such as the wings, legs, antennæ, etc., will be found neatly laid along each side of the "tongue," or proboscis, which latter extends down the centre. All these are separately encased, but by reason of the shell mentioned in the remarks on the caterpillar, they appear to be welded together. When, however, the butterfly is ready to emerge, the shell of the chrysalis is split along the thorax and at the lower edge of the wing-cases, and the insect is then able to release itself from the pupal trappings. This breaking open of the chrysalis shell is termed dehiscence (dehisco, "to split open"), and the manner in which it is effected varies in different species. The emergence of a butterfly from the chrysalis is always an interesting operation to observe, and every one should make a point of watching the process, so that he may obtain practical knowledge of how the thing is done. A photograph of it will be found in the description of the Wall Butterfly.
The Butterfly.
Having safely cleared itself free of the chrysalis shell, the butterfly makes its way to some suitable twig, spray, or other object, from which it can hang, sometimes in an inverted position, whilst a very important function takes place. This is the distention and drying of the wings, which at first are very weak and somewhat baggy affairs, although the colour and markings appear upon them in miniature. All other parts of the butterfly seem fully formed, but the helpless condition of the wings alone prevent it as yet from floating off into the air. In a remarkably short time, after the insect has settled to the business, the fluids from the body commence to flow and circulate through the wings, and these are seen gradually expanding and filling out until they attain their proper size. Occasionally there is some obstruction to the equal distribution of the fluids, and when this occurs a greater or lesser amount of distortion, or cockle, in the wing affected is the result. When the inflation is completed the wings are kept straight out for a time; they are then motionless, but all their surfaces are well apart. The wings being now fully developed, the further flow of fluid appears to be arrested. It has been stated by some authorities that this fluid is fibrin held in solution, and that when the work of expansion has been accomplished, the watery medium evaporates, leaving the fibrin to harden, and so fasten together the upper and lower membranes of the wing and to fix the veins, or nerves, in their proper position. Mayer, a specialist on these matters, referring to the expansion of the wings, remarks that the blood [the fluid previously mentioned] forced into the freshly emerged wing would cause it to become a balloon-shaped bag if it were not for fibres that hold the upper and lower walls closely together. The fibres referred to, he states, are derived from those hypodermic cells which do not contribute to the formation of scales, but are stretched out from one wall of the wing to the other.
Fig. 6.
Head of Butterfly.