128 J. r. Hii-L. 



body ((/. />.). CD. viv.. 1, 15 . vii . "01. f. Picro-nitro-osmie, iron-luema- 

 toxylin.) 



Figs. 19 and 20.— Plioto-microgmplis ( X about 70) of 4-celled eggs 

 taken immediately after transference to Perenyi's fluid. Fig. 19. side 

 view, showing yolk-body (y. b.) ; fig. 20, polar view. Diameter of entire 

 egg about -3.5 mm. (D . viv., 14 B, 18 . vi . '02. Perenyi.) 



Fig. 21.— Photo-micrograph (x about 70) of another -i-celled egg, 

 from the same batch as the preceding, seen from lower pole. 



Fig. 22.— Photo-micrograph (x 150) of section of 4-celled egg of 

 same batch as those of figs. 19 and 20. The two right and the two 

 left blastomeres respectively form pairs, so that the plane of the first 

 cleavage is parallel with the sides of tb.e phite, that of the second with 

 the top and bottom of the same. The two left blastomeres are stiU 

 connected by a narrow cytoplasmic bridge. Thickness of shell, 

 •0072 mm. 



Fig. 23. — Photo-micrograj)!! ( x 150) of a vertical section through 

 a 4-celled egg. '35 mm. in diameter, showing two of the blastomeres 

 and a small portion of the yolk-body {y. h.). Note, as in fig. 22, the 

 marked differentiation in the cytoplasm of the blastomeres. (D. viv., 

 4, 27 . vi . "01. Picro-nitro-osmic, iron-hajmatoxylin.) 



Figs. 24 and 25. — Photo-micrographs ( x 140) of horizontal sections 

 through a 16-celled egg. "38 mm. diameter, fig. 24 showing the eight 

 larger, more yolk-rich cells of the lower (non-formative) ring, and fig. 25 

 the eight smaller, less yolk-rich cells of the upper (formative) ring. 

 Shell '0075 mm. in thickness, yolk-body (not included in the figures) 

 •11 X -10 mm. in diameter. (D. viv.. 3 B, 26 . vi . '01 ; 15. f and |. 

 Picro-nitro-osmic and iron-heematoxylin.) 



Fig. 26. — Photo-micrograph (x 140) of a vertical section of an egg 

 of the same batch and size as that represented in figs. 24 and 25. but 

 witli seventeen cells— formative = 9 (6 -f [1 x 2] -f 1) in division ; 

 non-formative = 8. Two of the formative cells (/. c.) of the upper ring 

 are seen enclosing between them the faintly marked yolk-body {y. h.), 

 and below them two of the much more opaque non-formative cells 

 {tr. ect.) of the lower ring. 



PLATE 3. 



Fig. 27. — Photo-micrograph (x about 76) of the just completed 

 blastocyst, ^39 mm. in diameter. From a spirit specimen. The dark 

 spherical mass (eg.) in the blastocyst cavity is simply coagulum, pro- 

 duced by the action of the fixative (picro-nitro-osmic acid) on the 

 albuminous fluid which fills the blastocyst cavity. (D . viv.. 2 B, 

 16 . vii . '01.) 



