560 



ZOOLOGY 



but the dorsal surface of the posterior thoracic and abdominal 

 regions : in order to bring the parts into their adult position, the 

 abdomen must be supposed to be lifted up and turned backwards. 

 In the meantime the post-mandibular appendages are formed 

 in regular order from before backwards : the eye-stalks appear 



7 O CCfl 



abet 



Figs. 445 .and 446. — Sections of embryos of Astacus. A, Nauplius-stagc (rj. Fig. 444 ; B, after 

 development of thoracic appendages (ef. Fig. 447). abd. abdomen ; an. anus ; br. brain ; 

 ect. ectoderm; end. endodcrm ; ent. enteron ; lit. heart; mes. mesoderm; mes.' splanchnic 

 layer of mesoderm ; mth. mouth ; pedm. proctodwum ; stdm stomod«um ; th. abd. thoracico- 

 abdominal rudiment ; v. nv. cd. ventral nerve-cord. (From Korschelt and Hcider, after 

 Rcichenbach.) 



(Fig. 447, A), as well as the labrum (/.), and a fold on each side 

 of the thorax, which is the rudiment of the carapace (7s), "and this 

 gradually extends dorsal ly until it meets with its fellow of the 

 opposite side and covers in the cephalothorax. The embyro now 

 consists of a nearly globular cephalothorax with a small abdomen 



