630 



ZOOLOGY 



SECT. 



number of narrow transverse lines which indicate the boundaries 

 of the future segments. 



Rudiments of appendages (Figs. 503, 504) appear on the head 

 and thorax, and a series aiso appears on the abdomen ; all of the 

 latter, however, subsequently disappear with the exception of the 

 last pair, which give rise to the cerci. The segment on which the 

 rudiments of the antennae appear is at first post-oral in position, 



FIG. 503 Ventral plate of embryo Cockroach 



(Blatta germanica),- 1 isolated from the 

 yolk. as. amnion and sei'osa ; at. antennary 

 lobe ; cfjl. brain ; r/>/. caudal plate ; lb. 

 labrum ; md. mandible ; u;i, mx 2 , first and 

 second maxillfe ; /<!, //-, ]>'', legs. (After 

 Wheeler.) 



FIG. 504. Embryo Cockroach just after the 

 rupture of the amnion and serosa, lateral 

 view of entire egg. Letters as in preceding 

 figure. In addition, -at, fatty body ; ast. 

 caudal styles ; b. cephalic end of yolk ; oc. 

 eye. (After Wheeler.) 



but subsequently becomes fused with a pre-oral segment (pros- 

 tomium), so that the antennae acquire their permanent pre-oral 

 position only secondarily. The prostomial segment, the antennary 

 segment, a segment devoid of appendages, the segment bearing 

 the rudimentary mandibles, and those bearing the two pairs of 

 maxillae, all unite to form the head of the adult. 



Then follows the appearance of the larval membranes. On 

 either side 'arises a fold of the blastoderm ; and the two folds 

 grow inwards and eventually unite over the body of the embryo, 



