Fig. 57. —Aitacvs flHriuliHa. — Diagrammatic sections of emhr^'os ; partly after Reiehenbach, partly 

 original ( X 20). A. An ovum iii which the blastoderm is just formed. B. An ovum in which 

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

 taken place. (This nearly answers to the stage represented in fig. 68, A.) C. A longitudinal 

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

 gut have ajipeared. (This nearly answers to the stage rejiresented in fig. 58, E.) D. A similar 

 section of an embryo in nearly the same stage of development as that represented in C, fig. 59. 

 E. An embryo just hatched, in longitudinal section ; a, anus ; 6/, blastoderm ; hp, blasto- 

 pore ; f, eye ; ep.h., epiblast ; /f7, fore-gut ; /</', its cesophageal, nnd fg^, its gastric portion; 

 h, heart : hn, hind-gut ; rx, mouth ; ing, hypoblast, archenteron, or mid-gut ; r, yelk. The 

 dotted portions in D and E represent the nervous system. 



