PLATE 10 



EXPLANATION OF FIGURES 



(^lagnification of all of the figures X 37o.) 



28 Portion of formative region of l)lastocyst No. 43 (9). EXT,^ entodermal 

 mother cell in the blastocyst wall; EXT, ])rimitive entodermal cell. Both cells 

 are much darker than the adjacent ectodermal cells. See F, text figure 6, for 

 outline sketch of entire section of blastocyst. 



29 and 30 Adjoining sections through the embryonic area of blastocyst No. 

 43 (8), shown in outline in H, text figure 6. EXT,^ primitive entodermal cell 

 dividing from an entodermal mother cell; M, large cell in mitosis. This cell 

 contains a large fat spherule shown in section in figure 30. 



31 Section through embryonic area of specimen No. 40 (2). (Cf. outline 

 sketch B, text figure 6. EXT,^ entoderm cell being given off from entodermal 

 mother cell situated in the wall of blastocyst; EN T, -large cell dividing obliqueh- 

 to surface; 0, elongate cells and nuclei, with axes oblique to surface of blastocyst. 



32 Section through embryonic area of D text figure 6, specimen No. 40 (4). 

 EXT} entodermal mother cell which has migrated from its position in the wall 

 of the blastocyst. 



33 and 34 Two sections of blastocyst No. 40 (1), shown in outline in E, text 

 figure 6. EXT ^ primitive entoderm cell just divided from entodermal mother 

 cell and pushed out underneath the superficial ectodermal cell. 



35 Section through middle of the embryonic area of blastocyst No. 43 (7), 

 shown also in G, text figure 6. The area has thickened on account of rapid cell 

 division at this point, nearly every section of the series containing one or more 

 cells in mitosis. 



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