132 J. P. HILL. 



the blastomeres of the S-celled stage have ah-eady divided (4 + 4x2) 

 = 12. From a spirit specimen and from same batch as preceding. 



Fig. 59. — Drawing ( X about 88) of a 31-celled egg ('STS mm. diameter) 

 as seen from the lower pole. From a spirit specimen and from the same 

 batch as the preceding. The irregular body in the Idastocyst cavity is 

 formed by coagulum. Formative cells = 16; non- formative = 14 + 1 

 in division. 



Fig. 60. — Drawing ( X about 88 ) of another 31-celled egg ('375 diameter) 

 from the same batch as the preceding. Side view. 



Fig. 61. — Drawing (X 100) of an entire lilastocyst (39 mm. diameter) 

 from the same batch as those shown in figs. 27-29. 



Fig. 62. — Drawing (x abont 80) of an entire Idastocyst ('4 mm. 

 diameter) from the same batch as the preceding. 



Fig. 63. — Drawing (X 80 of an entire blastocyst ('6 mm. diameter) 

 made from a photograph taken directly after transference of the speci- 

 men to the fixing fluid. Cells of lower hemisphere with much more 

 marked perinuclear areas of dense cytoplasm than those of the npper. 

 D. viv., 2, 11 . vii . "01.) 



Fig. 64. — Section of tlie wall of a Idastoeyst, 2'4 mm. diameter 

 (X 630). (D. viv., 7 . vi . '01.) 



Figs. 65, 66, 67. — Drawings (X 630) of small portions of in toto 

 preparations of the formative region of 6 . 7 . '04 l)lastocysts to demon- 

 strate the mode of origin of the primitive entodermal cells {eut.. fig. 67). 

 Fig. 65 shows a dividing entodermal mother-cell in position in the 

 nnilaminar wall, surronnded by lai-ger lighter staining cells (prospective 

 embryonal ectodermal cells). In fig. 66 is seen a corresponding cell, a 

 portion of whose cell-body has extended inwards so as to underlie 

 (overlie in figure) one of the ectodermal cells of the wall. In fig. 67 

 are seen two entodermal cells, evidently sister-cells, the j)roducts of the 

 division of such a cell as is seen in figs. 65 or 66. One of them (the 

 upper) is still a constituent of the nnilaminar wall, the other (ent.) is a 

 primitive entodermal cell, definitely internal. (D . v i v ., 6 . 7 . "04. Picro- 

 nitro-osmic, Ehrlich's ha3matoxylin.) 



PLATE 7. 



Figs. 68, 69, 70. — Drawings (x 630) of portions of preparations 

 similar to the above. For description see text. (D. viv., 6. 7, '04.) 



Fig. 71. — Drawing (x about 630) of a portion of an in toto pre- 

 paration of the formative region of an '01 blastocyst showing two 

 primitive entodermal cells, one of them in division. (D. viv., /3, 

 25 . vii . '01. Picro-nitro-osmic and Ehrlich.) 



