650 



ZOOLOGY 



adults in their food and mode of life ; very generally the jaws are 

 adapted for biting, even when the mouth of the adult is suctorial. 



!. 520.— A— E, ventral view of five stages in the development of Hydroplillus. a aiid b, 

 puiiits at which the blastopure first closes ; af. edge of the amniun fold ; af, caudal fold ; af", 

 Xmired head-fold ; an. antenna ; ea, terminal segment ; g, pit-like invagination to form the 

 rudiment of the amnion cavity ; k, procephalic lobes ; v, gruove-like medio-ventral in- 

 vagination ; .1, germinal bands covered by the amnion. (From Lang, after Heider.) 



B 



Fig. 530.—^ and M, later stages of the embryo of Hydrophilus with the rudimeDts of the 

 extremities ; in B the abdominal appendages are visible, a. anus ; an. antenna ; gr, rudiment 

 of the ventral nerve-chain; m. mouth; md. mandible; mx^, iirst maxilla; «i3:2, second 

 maxilla ; pi, k. 'Ps, thoracic legs ; pi, P5, J'7i PS. rudiments of the appendages of the first, 

 second, fourth, and sixth abdominal appendages ; st. stigmata ; vk, prostomium. (From 

 Lang, after Heider.) 



After a longer or shorter period passed in this larval condition, in 

 which it is^usually active and very voracious, the young Insect 



