XI 



PHYLUM ARTHROPODA 



601 



is applied to the metamorphosis of the majority of Insects, in 

 which the larva differs so completely from the i inn (/<->. or perfect 



eo- 



FIG. 491. A E, ventral view of five stages in the development <>f Hydrophilus; . and /;, 

 points at which the blastopore first closes ; /'. edge of the aniiiion fold ; nf, caudal fold^; nj", 

 paired head fold ; an. antenna ; cs, terminal segment ; f/, pit-like invagination to form the 

 rudiment of the amnion cavity ; A-, procephalic lobes ; /, groove-like medio- ventral in- 

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



B 



FIG. 492. 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; /,i. mouth; 'Mil. mandible; m.c 1 , first maxilla; <.<'-', second 

 maxilla; pi, i;, p 3 , thoracic egs ; j) 4 , p- } , j> 7 , _/;<,, nidiments of the appendages of the first, 

 second, fourth, and sixth abdominal appendages; xt. stigmata; ck, prostomiiim. (Fn>m 

 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 



