oHO 



ZOOLOGY 



but the dorHal 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 apj)ear 



pcdmT th^ccJbd^^S^"'^ 



Figs. 445 and 446.— Sectiuns of embryos uf Astacus. A, Nauplius-stage (rj. Fig. 441 ; B, after 

 development of thoracic appendages (r/. Fig. 447). ohd. abdomen ; da. anus ; hr. brain ; 

 cct. ectoderm; t'<K^ endoderui ; tni. enteroii ; lit. heart; v/tts, mesoderm; mn^.' splanchnic 

 layer of mesoderm ; mth. mouth ; -iH-din. proetuda^uni ; Ud,ii btumodfeum ; th. ab'l. thoraeico- 

 abdominal rudiment ; v. no. cd. ventral nerve-cord. (From Korschelt and Huider, after 

 Reich enbaeh.) 



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

 uf the thorax, which is the rudiment of the carapace (^5), 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 



