PLATE 13 
EXPLANATION OF FIGURES 
Résumé of stages in the development of the opossum egg as drawn from sections 
of representative specimens from the ovarian egg to the primitive streak stage. 
x 50. 
1 Ovarian egg from specimen No. 28; Hermann’s fluid. 
2to 5 Respectively the following tubal ova: No. 76 (8), Hill’s fluid; No. 
56 (4), Bouin’s; No. 351 (1); Hills; No. 313’ (1), Bouin’s. 
6 Unsegmented uterine egg No. 287 (1); Hill’s fluid; 5 wu. 
7 2-celled ovum No. 203 (4); thirteenth section (total 20); 5 yu. 
8 4-celled ovum No. 203 (5); tenth section (total 21); Hill’s fluid; 5 p. 
9 14-celled ovum No. 193 (6); eighth section (total 17); aceto-osmic- 
bichromate. 
10 Just completed blastocyst No. 191 (2); eleventh section (total 18); 32 
cells; Bouin; 6 yu. 
11 63-celled blastocyst No. 50 (8), of which one of the two entoderm mother 
cells is shown in fig. 5, pl. 16; ninth of 17 sections; Hill’s fluid. 
12 Egg No. 356 (4), the seventeenth section (total 25); compare figs. 6 and 7, 
oll, I/3 (0 ja. 
13 Blastocyst No. 194’ (3); ninth section of vesicle (total 34); fifth section 
of embryonic area (total 13); aceto-osmic-bichromate (?); 5 uw. 
14 No. 352 (7); detail invfig. 8, pl. 21, q. v. 
15 Egg No. 339 (5); thirtieth section of blastocyst (total 65); not perfectly 
normal; one-half strength Bouin; 5 pw. 
16 No. 299’ (5), shown in toto in fig 1, pl. 6; sixty-second section of egg 
(total 122) and thirty-fifth section of blastocyst (total 83); Hill’s fluid; 5 uz. 
17. No. 306’ (2), also shown in fig. 2, pl. 20, q. v. 
18 Bilaminar blastocyst No. 189 (6), the embryomie area of which is shown in 
fig. 4 pla21> qv. 
19 Bilaminar blastocyst No. 55 (19), showing (at right) a mass of cells at 
lower pole sixty-sixth section of egg (total 139); twenth-fourth section of em- 
bryonic area (total 77); Bouin. 
20 Bilaminar blastocyst No. 189’ (10) approaching time of mesoderm forma- 
tion; 130th section of egg (total 282); ninety-third section of embryonic area 
(total 165); vesicle wall very thin; egg slightly damaged. 
21 Eeg No. 353’ (6), blastocyst with about 140 mesodermal cells; 1.6 mm. 
in aleohol with embryonic area 1.1 mm.; ninety-second section (total 205); M. 
mesodermal cells, Bouin; 6 pw. 
22 Eee No. 346’ (6); section taken through primitive steak; 1.5 mm. in 
diameter in aleohol; embryonic area 1.1 mm.; Bouin; 5 «; compare fig. 4, pl. 2. 
122 
