560 



ZOOLOGY 



SECT. 



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 



ntes' 



ftiCS 



br 



stdrrv 

 ntth 



FIGS. 445 and 446. Sections of embryos of Astacus. A, Nauplius-stage (<rj. Fig. 444 ; U, after 

 development of thoracic appendages (r/. Fig. 447). abd. abdomen ; an. anus ; 6r. brain ; 

 ect. ectoderm; end. endoderm ; ent. eiiteron ; ht. heart; mes. mesoderm ; mes.' splanchnic 

 layer of mesoderrn ; inth. mouth ; pcdm. proctodamm ; stdm. stomodseuru ; th. ubd. thoracico- 

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

 Reichenbach.) 



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

 of the thorax, which is the rudiment of the carapace (te), and this 

 gradually extends dorsally 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 



