PATHOLOGIC OVA, ALBINO RAT 371 
of this rat ten blastodermic vesicles, two of which are repro- 
duced in A and B of figure 24, Part I, as showing typically early 
stages of the anlage of the ectoplacental cone and entypy of the 
germ layers. The ovum shown in figure 5 is found in a decidual 
erypt which is in very close proximity to the one containing the 
vesicle figured under B of figure 24, Part I, the two crypts being sep- 
arated by a distance of approximately 1.3 mm., while the distance 
between decidual crypts is normally 1 ecm. to 1.5 em. The de- 
cidual crypt lodging the abnormal ovum presents a normal ap- 
pearance, resembling very closely in form, depth and structure 
Fig. 6 Two ova of the albino rat, interpreted as evidencing retarded or 
irregular formation of the segmentation cavity. >< 200. <A, rat No. 90, 6 days, 
17 hours, after the beginning of insemination. B, rat No. 90, 6 days, 17 hours, 
after the beginning of insemination. p.ect., parietal or transitory ectoderm; 
y.ent., yolk entoderm; p.ent., parietal entoderm. 
of the surrounding decidua, the crypt and decidua enclosing the 
adjacent normal vesicle figured in B of figure 24, Part I. The 
abnormal ovum in question appeared to have proceeded nor- 
mally in segmentation, its constituent cells being of about the 
size and structure of the cells of normal vesicles taken the early 
part of the seventh day after insemination. The cell-mass en- 
closes a relatively small cavity which may be regarded as an ab- 
normally placed segmentation cavity, in that its position is not 
eccentric, and that it is surrounded on all sides by more than one 
layer of cells. There is thus no differentiation of floor and roof 
as in normal blastodermic vesicles, and no development of ecto- 
placental cone and egg-cylinder as in the other ova obtained from 
