700 



TEXT-BOOK OF ENTOMOLOGY 



two later stages, the great differences between the first and the last 

 two being apparently due to their parasitic mode of life, the larva 

 spending its second stage within its host, involving an existence in a 

 cell with a high temperature, an uninterrupted supply of rich,. stimu- 

 lating food, and a comparatively sedentary mode of life compared 

 with that of the triungulin at the beginning of its existence. It is 

 quite obvious that the hypermetamorphosis is primarily due to a 

 great change in its surroundings, i.e. the parasitic mode of life of 



FIG. 647. First larval stage of Bruchus pisi : a, egg in pea-pod ; b, cross-section of opening of 

 mine ; c, young larva and opening on inside of pod by which it has entered, enlarged ; d, d, d, eggs, 

 natural size ; e, 1st larval stage ; /', a leg of same ; g, prothoracic spinous processes. After Riley. 



the beetle, habits of very rare occurrence in the Coleoptera, numerous 

 in species as they are. 



In this connection attention may be drawn to a supernumerary 

 larval stage observed by Riley in the pea- and bean-weevils (Figs. 

 646 and 647). The larva on hatching has long slender legs, though 

 differing from those of an ordinary coleopterous larva in having but 

 three joints (j, g, Ji). This stage is very short, and the legs tempo- 

 rary, as, after entering the bean or pea, it casts its skin, losing its 

 legs, and assuming the vermiform shape of the second larval stage. 

 In this case the change from a pedate to an apodous larva is plainly 

 enough due to the change from an external feeder, like a chrysomelid 

 larva, to a larva leading a boring, internal, almost quiescent life. 



