

Fig. 47 



A to Jif. Various stages of the development of Ainphloxns lanceolatus (mostly 

 after Hatschek ; //, /, K^ and L modified after Morgan). A^ the unsegmented 

 ovum; 5, the first two blastomeres resulting from the first cleavage ; C, stage 

 with four equal blastomeres; Z>, eight-cell stage consisting of four smaller 

 cells (micromeres) above and four larger cells (niacromeres) below; E^ sixteen- 

 cel] stage ; F^ optical section of thirty-two' cell stage showing the segmentation 

 cavity or blastoccele, opening. to the exterior above and below ; (P, a later stage, 

 the blastoccele completely closed in ; //", a blastula shortly before invagination; 

 J, commencement of invagination of the larger granular cells of the lower 

 pole ; K^ gastrula, with widely-open blastopore ; Z, later gastrula in which 

 the blastopore has been narrowed by the folding together of the walls ; 

 M, embryo with neural plate and commencing neurenteric canal. ach^ 

 archenteron ; be, blastoccele ; bp, blastopore ; ec^ epiblast ; f«, hypoblast ; 

 mic, micromeres; fnac, macromeres ; nec^ neurenteric canal; «/, neural plate; 

 Pb, polar bodies. 



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