PHYLUM ARTHROPODA 



601 



applied to the metamorphosis of the majority of Insects, in 

 which the larva differs so completely from the imago, or perfect 



' 





fc 



y-W 



FiG. 491. A E, ventral view of five stages in the development of Hydrophilus j a and b, 

 points at which the blastopore first closes ; af. 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; /, groove-like medio-ventral in- 

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



B 





)2. A 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 ; -ni. mouth ; md. mandible ; mrf , first maxilla ; mx*, second 

 maxilla ; pi, p-2, p%, thoracic egs ; p, p, p?, pg, rudiments of the appendages of the first, 

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

 Lang, after Heider.) 



Insect, in external form, the nature of the appendages, and the 

 internal organisation, that there is need of a quiescent or pupa 



