//•'/ 5>^ To/ 



Fio. 57.^Astacvs fluriatilis. — Diagrammatic seetions of embryos ; partly after Reicheiibacli, partly 

 original (x2()). A. Au ovum in wliicli the blastoderm is just formed. B. An ovum in which 

 the invagination of the blastoderm to constitute the hypoblast or rudiment of the mid-gut has 

 taken place. (This nearly answers to the stage represented in fig. 58, A.) C. A longitudinal 

 section of an ovum, in which the rudiments ot the abdomen, of tlie hind-gut, and of the fore- 

 gut have ap])eared. (This nearly answers to the stage represented in lig. 08, E.) 1). A similar 

 section of an cmbi'yo in nearly the same stage of development as thut represented in C, fig. 59. 

 E. An embryo just hatched, in longitudinal section ; a, anus ; bl, blastoderm ; bp, blasto- 

 pore ; c, eye ; ep.b., epiblast ; /gr, fore-gut;/'/', its CE.sophageal, and /g^, its gastric portion; 

 h, 'heart. ; hfi, hind-gut ; m, mouth ; mg, hypoblast, archenteron, or mid-gut ; r, yelk. The 

 dotted portions in D and E represent the nervous system. 



