650 



ZOOLOGY 



SECT. 



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. 



A B _ r . D E 



Fio. 529. A E, ventral view of five stages in the development of Hydrophilus. a and b, 

 points at which the blastopore first closes ; a/, edge of the amnion fold ; a/', caudal fold ; af", 

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

 rudiment of the amnion cavity ; k, procephalic lobes ; r, groove-like medio-ventral in- 

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



B 



FIG. 530. A and B, later stages of the embryo of Hydrophilus with the rudiments of the 

 extremities ; in.# the abdominal appendages are visible, a. anus ; an. antenna ; g, rudiment 

 of the ventral nerve-chain ; m. mouth ; Hid. mandible ; mx 1 , first maxilla ; mx z , second 

 maxilla; p\, p& Ps, thoracic legs; p 4 , p 5 , p 7 , PQ, rudiments of the appendages of the first, 

 second, fourth, and sixth abdominal appendages ; st. stigmata ; rA-, 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 



