96 NATURAL HISTORY OF AQUATIC INSECTS CH. I 



substance of the root, appear upon the plant when the; 

 cocoon is detached, and it is probably from this source 

 that the pupa derives its supply of air. Wounds in 

 the living tissues of the plant are as a rule quickly 

 repaired by a corky growth, but Schmidt-Schwedt 

 found that this was not the case with the holes bored 

 by the Donacia-larva in the roots of the water-lily. 

 They remain open so long as the access of v/ater is 

 precluded by the cocoon, and only become closed by 

 cork when the cocoon is torn open by the emergence 

 of the Beetle. The under side of the adult Insect is 

 protected from wetting by a close covering of silky 

 hairs. 



The perfect Beetle appears in early summer ; the 

 larva; feed until autumn, and then pupate. The per- 

 fect Insect is believed to remain throughout the winter 

 in its pupal cocoon, for cocoons opened at this season 

 generally contain fully developed Insects and not 

 pupae. 



