_The Transformation from the Chrysalis to the Imago._--The perfectly developed insect is known technically as the _imago_. When the time of maturity in the chrysalis state has been reached, the coverings part in such a way as to allow of the escape of the perfect insect, which, as it comes forth, generally carries with it some suggestion of its caterpillar state in the lengthened abdomen, which it with apparent difficulty trails after it until it secures a hold upon some object from which it may depend while a process of development (which lasts generally a few hours) takes place preparatory to flight. The imago, as it first emerges, is provided with small, flaccid wings, which, together with all the organs of sense such as the antennæ, require for their complete development the injection into them of the vital fluids which, upon first emergence, are largely contained in the cavities of the thorax and abdomen. Hanging pendant on a projecting twig, or clinging to the side of a rock, the insect remains fanning its wings, while by the strong process of circulation a rapid injection of the blood into the wings and other organs takes place, accompanied by their expansion to normal proportions, in which they gradually attain to more or less rigidity. Hardly anything in the range of insect life is more interesting than this rapid development of the butterfly after its first emergence from the chrysalis. The body is robbed of its liquid contents in a large degree; the abdomen is shortened up; the chitinous rings which compose its external skeleton become set and hardened; the wings are expanded, and then the moment arrives when, on airy pinions, the creature that has lived a worm-like life for weeks and months, or which has been apparently sleeping the sleep of death in its cerements, soars aloft in the air, the companion of the sunlight and the breezes. ANATOMY OF BUTTERFLIES The body of the butterfly consists of three parts--the head, the thorax, and the abdomen. [Illustration FIG. 29.--Head of milkweed butterfly, stripped of scales and greatly magnified (after Burgess): _v_, vertex; _f_, front; _cl_, clypeus; _lb_, labrum, or upper lip; _md_, mandibles; _a_, antennæ; _oc_, eyes; _tk_, spiral tongue, or proboscis.] [Illustration FIG. 30.--Cross-section of the sucking-tube of the milkweed butterfly, to show the way in which the halves unite to form a central canal (_c_): _tr_, tracheæ, or air-tubes; _n_, nerves; _m_, _m^3_, muscles of one side. (Magnified 125 diameters.) (Burgess.)] [Illustration FIG. 31.--Longitudinal section of the head of the milkweed butterfly: _cl_, clypeus; _mx_, left maxilla, the right being removed; _mfl_, floor of mouth; _oe_, oesophagus, or gullet; _ov_, mouth-valve; _sd_, salivary duct; _dm_ and _fm_, dorsal and frontal muscles, which open the sac. (Magnified 20 diameters). (Burgess.)]