PLATE 21 
EXPLANATION OF FIGURES 
The 1-mm. bilaminar blastocyst. 
1 Egg No. 306’ (3); 0.85 mm. in diameter in alcohol; 44th section of embryonic 
area (total 70) and the 84th section of vesicle (total 135); Bouin; 5u. X 50. 
1A Embryonic area (XX) of same section. X 200. 
2 Egg No. 55 (20); 0.87 mm. in diameter in alcohol; 57th section of vesicle 
(total 121) and 33d section of embryonic area (total 77); O, pocket in tropho- 
blastic ectoderm; Flemming; 64. X 50. 
2A Embryonic area (XX) of same section; at A, unusual crowding of ecto- 
derm. XX 200. 
3 Egg No. 339’ (3); 0.85 mm. in alcohol; 64th section of vesicle (total 118) 
and 45th section of embryonic area (total 71); 0, pocket in ectoderm; half- 
strength Bouin; 64. X 50. 
4 Embryonic area (XX) of egg No. 189 (6), shown in fig. 18, pl. 13; 74th 
section of embryonic area (total 94); 1.02 mm. in alcohol; Hill’s fluid; 5 u. X 200. 
5 Embryonic area (XX) of egg No. 343 (4), about 1.0 in alcohol (compare 
fig. 5, pl. 2, and fig. 9 below); 99th section of vesicle (total 189) and 67th of 
embryonic area (total 126); Bouin; 5 yu. XX 200. 
6 <A portion of trophoblastic area of a 1.0 blastocyst No. 55 (6), showing 
remnant of albumen; compare fig. 10, pl. 22; Hill’s fluid. > 200. 
7 and 7A Sections through embryonic and trophoblastic areas of ovum 
No. 285’ (6); 65th section of vesicle (total 119) and 26th through embryonic area 
(total 65); Hill’s fluid; 6. X 200. 
8 Embryonic area (XX) of ovum No. 352 (7); 35th section of egg (total 80); 
24th section of vesicle (total 49) and 13th section of embryonic area (total 21); 
in aleohol egg measured 0.585 mm. through shell membrane and 0.325 * 0.370 
through vesicle; 64; Bouin. X 200. 
9 Surface view of a typical 1 mm. blastocyst, showing embryonic area; 
compare fig. 2, pl. 11, and fig. 3, pl. 10. X 16. 
10. Half-normal blastocyst No. 314 (3); Bouin; 5 4. X 200. 
138 
