200 ELEMENTS OF COMPARATIVE ZOOLOGY. 



these, three pairs are on the thoracic segments, while the 

 abdomen has from one to five pairs. These larvae, when 

 they hatch from the egg are small, but by feeding they 

 grow, increase in size being rendered possible by frequent 

 moltings of the skin. At last there comes a molt by which 

 the appearance is greatly changed and the pupal stage is 

 reached. In the pupa the abdominal legs are lost, the body 

 is shortened and covered with a harder skin, in which 

 one can trace the legs, antennae, and wings of the future 

 moth or butterfly, folded over the breast. Many caterpillars 

 of the moths, as a preparation for pupation, spin silken 

 nests or cocoons, the silk being the product of glands which 

 empty into the mouth. The pupae of butterflies have 

 usually no such silken protection, but are free. From the 

 fact that many of these butterfly pupae are marked with 

 patches and spots of gold, they are frequently called chry- 

 salides (sing, chrysalis). 



The pupal stage lasts for some time (months), during 

 which no food is taken and no motion possible except of 

 the abdominal rings; then the pupal skin is molted and 

 the perfect insect (imago) emerges. In those forms which 

 have a cocoon the silken threads are softened by fluids 

 secreted by the imago, and in some there are hooks at the 

 bases of the wings which aid in tearing an opening for the 

 escape of the moth. 



When the imago first comes out it is soft and flabby, and 

 the wings are soft bags. They are rapidly distended by 

 blood pumped into them, and, held expanded, are rapidly 

 dried by the air into efficient organs of flight. The 

 wings are covered with scales, and to these is the color- 

 pattern due. These scales are merely modified hairs like 

 those which cover the whole body. When removed the 

 wing is seen to have a framework of supporting " veins " 



