PLATE 22 
EXPLANATION OF FIGURES 
Advanced bilaminar blastocysts, to the beginning of mesoderm proliferation. 
Figs. 2, 4, and 9 represent eggs only a few minutes removed from the first appear- 
ance of mesoderm. 
1 Egg No. 193’ (4), similar to fig. 9 below; a 92nd section of egg (total 184) 
and 55th section of embryonic area (total 87); Hill’s fluid; 7. X 50. 
2. Egg No. 343’ (2), one of the five shown in fig. 6, pl. 2; 1.5 mm. in alcohol; 
embryonic area, 0.87 mm.; 130th section of vesicle (total 259) and 89th section 
through embryonic area (total 161); Bouin; 5 yu. X 50. 
3 Egg. No. 353 (4); several hours preceding first appearance of mesoderm; 
diameter 1.22 mm. in alcohol; 91st section of vesicle (total 135) and 53rd section 
of embryonic area (total 85); Flemming; 6. 50. 
3A and 3B Details of trophoblastic and embryonic areas, respectively, of 
same section. X 200. 
38C A detail of fig. 3B. X 500. 
4and4A Egg No. 189’ (1); 118th section of vesicle (total 200) and 62nd section 
of embryonie area (total 116); aceto-osmic-bichromate. X 50 and X 200. 
5 Embryonic area (XX) of egg No. 347’ (1); 1.1 mm. in alcohol; 74th section 
of vesicle (total 126) and 55th section of embryonic area (total 82); Flemming; 
Napa 200: 
6 Thick embryonic area (XX) of egg No. 360 (4); 71st section of vesicle (total 
176) and 41st of embryonic area (total 130); 7, thinning near middle; Hill’s fluid; 
5 pu. X 200. 
7 The 79th section through embryonic area (total 172) of egg No. 189’ (9). 
X 200. 
8 Large embryonic area of egg No. 189’ (4); 157th section of egg (total 311) 
and 59th section of area (total 169); Hill’s fluid; 54. XX 200. 
9 Drawing made from photograph of an egg in litter No. 193’; shows central 
light field in embryonic area; compare figs. 1 and 2, pl. 10. X 16. 
9A Section of ovum No. 193’ (2); 61st section of embryonic area (total 160). 
xX 200. 
9B and 9C_ Details of portions of fig. 9A. X 560. 
10 Portion of embryonic area of 1-mm. blastocyst No. 55 (6), showing yolk 
granules (Y) in ectoderm, and entoderm; compare group A with A, fig. 11. 
11 Surface view of some entoderm cells from below the embryonic area of 
egg No. 189’ (12), showing reaction of cells to yolk remnants (Y). 
12A and 12B Surface views, from within, of embryonic and trophoblastic 
areas of egg No. 189’ (11); entodermal nuclei (mostly the larger) are seen above 
the entoderm; embryonic area measures 0.96 mm.; aceto-osmic-bichromate. 
* 500. 
13 Defective blastocyst No. 88 (6) with large included blastomere; Hill’s 
fluid; 5 yu. > 200. 
14 Half-normal blastocyst No. 356 (2); Bouin; 54. X 200. 
140 
