DEVELOPMENT OF THE OPOSSUM 13 
blastocysts a little over 1 mm. in diameter; no preparations made of 
this litter (figs. 2 and 3, pl. 11*). 
No. 292. Caught with male in hollow log Jan. 13; isolated till 
operation, Jan. 17, 11 p.m; 10 eggs: of the 4 that were sectioned one 
is a defective 7-celled egg, the others normal blastocysts of 40 to 50 
cells with none or only one entodermal mother cell (fig. 5, pl. 1*; figs. 1 
Deore Tand.G, ple i6): 
No. 292’. Killed Jan..21, 10:40 p.m. (interval 4 days); 7 vesicles 
about 3 mm. in diameter, late primitive-streak stage; one unfertilized 
ege@; one degenerating young bilaminar blastocyst (fig. 6, pl. 1*). 
No. 293. Caught Jan. 17; Jan. 18, 8:00 p.m., 13 eggs: of the eight 
preparations made all are 4-celled except one 2-celled egg; in one case 
one blastomere, in two cases 2 blastomeres are in mitosis (fig. 1, pl. 2*; 
figs. 5 and 6, pl. 15). 
No. 293’. Killed Jan. 22, 7:30 a.m. (interval 33 days); 17 eggs: 8 
unfertilized, one defective; 8 bilaminar blastocysts like those sketched 
insiext meure. 3, , KH, (igs 2. pl: 2° )2 9 = 
No. 294. Caught Jan. 17; large skin wound on belly; Jan. 18, 8:30 
p.M., 15 eggs: 5 unfertilized, 8 with small rounded or irregular blasto- 
cysts at one pole, all rather abnormal; 2 apparently normal bilaminar 
blastocysts like F, text fig. 3 (fig. 1, pl. 11*). 
No. 294’. Killed Jan. 20, 7 a.m. (interval 343 hours); 14 eggs: 7 
unfertilized; one 1.4 mm. in diameter and 4 small degenerating blasto- 
cysts; 2 bilaminar blastocysts about 1.3 mm. in diameter, of which 
only one is perfectly normal. Thus both litters, 294 and 294’, were 
mostly abnormal (fig. 4, pl. 11*). No preparations were made of this 
litter. 
No. 298. First copulation Jan. 14, spermatozoa recovered from 
vagina; at 1 p.m., Jan. 15, the double spermatozoa had mostly divided. 
Jan. 20, 10: 15 a.m., 14 eggs, of which perhaps 10 are normal blastocysts; 
five preparations contain 60 to 120 cells each, showing earliest ento- 
dermal proliferation (fig. 7, pl. 2*; figs. 7 and 8, pl. 6; figs. 6 and 20, 
ple 16): 
No. 298’. Killed Jan. 23, 12 m. (interval about 33 days); 6 eggs: 4 
vesicles 4.25 and 4.9 mm. in diameter with medullary groove as long 
as primitive streak; 2 smaller vesicles and 2 unfertilized eggs (eggs in 
utero, fig. 8, pl. 2*). 
No. 299. Caught Jan. 19; Jan. 20, 8:15 p.m., 12 eggs, of which all 
of the 7 sectioned are normal 4-celled eggs with small blastomeres 
(ie 3) pli hess Grandetepl 3, ties. 13 and 14, pl. 15). 
No. 299’. Killed 11:30 p.m., Jan. 24 (interval 4 days, 3% hours); 14 
eggs: 6 apparently normal, nearly or quite completed bilaminar blas- 
tocysts; 3 abnormal blastocysts; 5 unfertilized eggs (fig. 4, pl. 1*; 
figs. 1 and 2, pl. 6; fig. 5, pl. 10; figs. 7 and 8, pl. 12; fig. 16, pl. 13). 
No. 303. Caught Jan. 19; Jan. 20, pseudopregnant, 7 degenerating 
eggs a week old (fig. 7, pl. 11*); killed Feb. 1, the mammary glands 
still very thick, almost as in pregnancy. 
