DEVELOPMENT 



Eruciform Larvae. The prevalent type of larva 

 holometabolous insects is the cruciform (Fig. 210, E-I), illus- 

 trated by a caterpillar or a maggot. Here the body is cylin- 

 drical and often fleshy; the integument weak; the legs, anten- 

 nse, cerci, and mouth parts reduced, often to disappearance; 

 the habits sedentary and the sense organs correspondingly re- 

 duced. These characteristics are interpreted as being results of 

 partial or entire disuse, the amount of reduction being propor- 

 tional to the degree of inactivity. Extreme reduction is seen 

 in the maggots of parasitic and such other Diptera as, secur- 

 ing their food with almost no exertion, are simple in form, 

 thin-skinned, legless, with only a mere vestige of a head and 

 with sensory powers of but the simplest kind. 



Transitional Forms. The cruciform is clearly derived 

 from the thy sanuri form type, as Brauer and Packard have 

 shown, the continuity between the two types being established 

 by means of a complete series of intermediate stages. The 



FIG. 211. 



Mmitispa. A, larva at hatching thysannriform; B, same larva just before first 

 moult now becoming cruciform. C, imago, the wings omitted; D, winged imago, 

 slightly enlarged. A and B after BRAUER; C and D after EMERTON, from Packard's 

 Text-Book of Entomology, by permission of the Macmillan Co. 



beginning of the cruciform type is found in Neuroptera, where 

 the campodeoid sialid larva assumes a quiescent pupal condi- 

 tion. The key to the origin of the complete metamorphosis, 



