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. 



B _ C _ D ^ E 



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

 points at which the blastopore first closes ; af. edge of the amnion fold ; af, 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 ; x, germinal bands covered by the amnion. (From Lang, after Heider.) 



B 



Fig. 530.-^4 and B, later stages of the embryo of Hydrophilus with the rudiments of the 

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

 of the ventral nerve-chain ; m. mouth ; md. mandible ; mx\ first maxilla ; nufi, second 

 maxilla; jt\, j>2> Pit thoracic legs; p±, p$, pj, py, rudiments of the appendages of the first, 

 second, fourth, and sixth abdominal appendages ; st. stigmata ; xk, 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 



