Plates 1 to 11 contain 82 figures nearly two-thirds of which are from photo- 
graphs of living eggs. Plates 1 and 2 show the development of nine litters for 
given periods of time. Plates 3 to 10 are arranged by stage of development, and 
the same stages are shown in drawings on plates 14 to 22. Plate 12 was drawn 
from 8 specimens as they appeared in the living state. Plate 14 is a résumé of 
the stages covered in this paper as drawn from sections. 
PLATE 1 
EXPLANATION OF FIGURES 
Photomicrographs of living eggs in Ringer’s solution; the ten figures show two 
litters from each of five different animals; figs. 1 to 9 X 8; fig. 10, natural size. 
1 Litter No. 320; 4-celled eggs. 
Litter No. 320’; interval 5} days; primitive-streak stage. 
Litter No. 299; 4-celled eggs. 
Litter No. 299’; interval 4 days, 3{ hours; blastocysts partly bilaminar. 
Litter No. 292; young unilaminar blastocysts containing 40 to 50 cells. 
Litter No. 292’; interval ‘4 days; primitive-streak stages. 
Litter No. 307; tubal ova with a little albumen on one side. 
Litter No. 307’; interval 5? days; unfertilized, fragmenting eggs; albu- 
men rather opaque. ‘ 
9 Litter No. 337; 8- to 16-celled eggs. 
10 Litter No. 337’; vesicles with primitive streak and very short medullary 
groove; photographed in open uterus, natural size. 
CON OD Ot e W LO 
GENERAL ABBREVIATIONS 
A, designates particular portions of HNT?, undifferentiated primitive en 
various drawings to which reference todermal cells (pls. 17 and 18) 
is made in the text ENT, flattened definitive entodermal 
ALB, albumen cells (pl. 16) 
ART, artifact 
C, coagulum 
CH, chromosomes 
GR, granulosa cells of discus proligerus 
O, ‘blister’ in trophoblastic ectoderm 
EMB.A, embryonic area PB, polar body 
EMB, ECT, embryonic ectoderm or SM, shell membrane 
entectoderm TR.A, trophoblastic or non-embryonic 
ENT, definitive eritoderm; in plate 18 aren 
it designates the limit of spread of pp ATC trophoblastic ectoderm 
entoderm; in plates 21 and 22 it re- ; 
F sae : V, vacuole 
fers to certain specialized entodermal 
X, placed at limits of embryonic area 
cells A : 
ENTA, entoderm mother cells in wall (junctional line) 
of blastocyst (pls. 16 and 17) XX, embryonic area of sections, junc- 
ENT',entoderm mother cells that have tional line of surface views 
migrated into cavity of blastocyst Y, yolk masses 
(pls. 16 and 17) ZP, zona pellucida 
98 
