PLATE 16 
EXPLANATION OF FIGURES 
The formation of entoderm initiated. All magnifications are X 200, except 
figs. 5 to 10 which are * 500. 
1 Completed blastocyst No. 191 (5); 34 cells; 9th section (total 24); Bouin; 
5 1 
2 Large blastocyst No. 50 (7); 70 cells, but no entoderm; 11th section 
(total 23); Hill’s fluid. 
3 Half-normal blastocyst No. 88 (18); 8th section (total 19); Hill’s fluid; 5 p. 
4 Half-normal ovum No. 344 (12); 6th section (total 16); half-strength 
Bouin; 5 wu. 
5 Portion of 6th section (total 17) through ovum No. 50 (8) showing entoderm 
mother cell ENTA; 63 cells including 2 entoderm mother cells in wall; Hill’s 
fluid; compare fig. 11, pl. 13. 
6 Portion of 8th section (total 22) of ovum No. 298 (5), showing entoderm 
mother cell leaving its place in blast. wall; 126 cells, of which 8 are free entoderm 
mother cells and several are in process of formation; Bouin, 5; ef. fig. 7 pl. 2. 
7 Portion of 6th section (total 22) of ovum No. 88 (9); 106 cells of which 11 
are free entoderm mother cells; Hill’s fluid; 5 u. 
8and9 Portions of the 10th and 12th sections (total 18) through ovum No. 88 
21); 70 cells, including 10 more or less detached entoderm mother cells; Hill’s 
fluid. 
10 Greater part of 4th section (total 15) through ovum No. 88 (23); 57 cells 
including the two detached entoderm mother cells here shown; Bouin. 
11 Blastocyst No. 88 (16), having 82 cells; 6 of the 10 entoderm mother cells 
are here shown; 11th section (total 20); section 15, fig. 4, pl. 7; Bouin, 5 yp. 
12 Ovum No. 838 (5), containing 53 cells, including the one large binu- 
cleated entoderm mother cell (?) here shown; 9th section (total 20). 
13° Ovum No. 356 (3), most retarded member of litter No. 356;about 100 
cells; 12th section (total 20); Bouin; 5 un. 
14 Ovum No. 344 (4); small blastocyst with numerous entoderm mother cells; 
8th section (total 18); Hill’s fluid; 5 wu. 
15 Longitudinal section of ovum No. 344 (11), showing definite polar differ- 
entiation; typical entoderm mother cells; 7th section (total 19); half-strength 
Bouin; 164 cells: 
Embyonic ent-ectoderm.............. 71-cells of which 7 are in mitosis 
Trophoblgstic ectoderm.............. 70 cells of which 8 are in mitosis 
mC Od erie 2.035 ine. een net arian eA Ce 23 cells of which 3 are in mitosis 
16and17 The 7th and the 16th sections (total 22) taken horizontally through 
ovum No. 344 (14), slightly more advanced than preceding; fig. 16, through 
embryonic area; fig. 17, through trophoblastic area; half-strength Bouin; 5 «; 193 
cells: 
Hmbryonic ent-ectoderm: 2-0. 5. 2000s ane se oe 76 cells, 8 in mitosis 
rophoblasticgechod ernie er rane 98 cells, 13 in mitosis 
HO COR IIE Franson RS eR ne ne A 19 cells, 1 in mitosis 
18 to 22. Reconstructions from blastocysts to show the polar distribution of 
entoderm mother cells. Fig. 18, ovum No. 88 (17), 103 cells, of which 6 are 
entoderm'mother cells; section indicated by parallel lines is shown in fig. 2, lee 
Fig. 19, ovum No. 83 (1), 111 cells, of which 4 are free entoderm mother cells. 
Fig. 20, ovum No. 298 (3), 124 cells, of which 4 are entoderm mother cells. Fig. 
21, ovum No. 88 (7), 87 cells, including 5 entoderm mother cells; the section in- 
dicated by lines is shown in fig. 3, pl. 6. Fig. 22, ovum No. 88 (11), 103 cells, of 
which 9 are more or less free entoderm mother cells and 7 of these are in mitosis. 
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