40 



ENTOMOLOGY. 



The Pupa. A few days (usually from one to three) before 

 assuming the pupa or chrysalis state, the caterpillar becomes 

 restless, stops eating, deserts its food, wanders about, and 

 if it is a spinner, such as the silk-worm or certain other 

 moths, spins a silken cocoon; or if a borer, makes one of 

 earth or chips, and then prepares for the change to the 

 pupa state. 



Cocoons are usually oval, and either compact and thick, 

 or loose and open like network. In the course of one 

 summer the beginner can collect a large number, and 

 realize how varied in form and structure they are. They 

 are usually spun out of a silken thread. The silky material 

 is formed in the silk glands-, two long tubes which lie on 

 the under side of the body of the caterpillar and open into 

 the under lip by a common duct; the little projection or 

 papilla out of which the silk passes is called the spinneret. 

 The silk is fluid before it is forced out, but becomes thread- 

 like on exposure to the air. 



Before changing, the body of the caterpillar becomes 

 shorter and thicker, and remains so for one or several days; 

 that of the saw-fly remains in this state through the winter. 

 During this period, called the semipupal stage, the pupa 

 develops, its skin separating from that of the larva. 



It should be borne in mind that the skin is composed of 



two layers; the under one 

 formed of cells and called the 

 hypodermis (Fig. 37), which 

 secretes the hard, chitinous, 

 structureless outer layer or 

 crust. The hypodermis of 

 the growing pupa tends more 

 and more to assume the shape 



FIG. 37. Cross section through the .p 1 1 ,] j.i, p T^iioplpo 



cuticula, C, and hypodermis, M. The 01 tne PUP'% and 

 setae or hairs,//, are articulated at nvi ,q nflmv nrrrona witliin 

 C with the cuticula; HZ, cell. The antt 



poison-glands at the base of the c l iar ,or e their shape, Until 

 bristles of some insects resemble 

 these.-From Judeich and Nitsche. fi na lly the old larval skill rup- 



tures along the back, and the pupa slips out of the rent. 



