PLATE 18 
EXPLANATION OF FIGURES 
Stages from the spreading of the entoderm to the just completed bilaminar 
blastocyst. Whole sections (figs. 5A, 6A, 7A) X 50; vesicles oniy & 200; ENT, 
limits of distribution attained by the entoderm; ENT°, undifferentiated primi- 
tive entoderm not yet spread. 
1 Blastocyst No. 48 (7); 10th section through embryonic area; Bouin. 
2 Blastocyst No. 352 (12); 42nd section through egg (total 98), 33d, section 
through vesicle (total 80), and 18th section through embryonic area (total 50); 
half-strength Bouin; 5 uw; compare fig. 1, pl. 9. 
3 Blastocyst No. 40 (1); 15th section through embryonic area (total 30); 
Hill’s fluid. 
4 Blastocyst No. 40 (2); the 19th section through embryonic area (total 36); 
Carnoy. 
5A and 5 Blastocyst No. 347 (2); earliest stage of the completed bilaminar 
blastocyst; 22nd section through vesicle (total 57); Bouin; 7 u; compare fig. 5, 
pl. 9. 
6A and6 Blastocyst No. 339 (8). Fig. 6A, 66th section of vesicle (total 94) 
and 37th section of embryonic area (total 51); fig. 6, 68th section of vesicle; Bouin; 
5 w; compare fig. 6, pl. 9, and fig. 2, pl. 6. 
7A Egg No. 347 (1); 52nd section through egg (total 127); 46th section through 
vesicle (total 103); entoderm spread to equator. 
7 Blastocyst No. 347 (4); nearly the same stage as fig. 7A; 32nd section 
through vesicle (total 90); Bouin; 7 x. 
8 Blastoeyst No. 175’ (2); 9th section through embryonic area (total 25) 
and 30th section through vesicle (total 56); aceto-osmic-bichromate; 6 u. 
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