PATHOLOGIC OVA, ALBINO RAT 389 
b. Such in which a single abnormal or pathologic ovum is 
found in the same uterus along with an average number of 
normally developed ova. 
When all the ova in a given uterus show abnormality, the 
presumption seems warranted that the underlying cause of the 
abnormality is to be sought in an altered or pathologic condition 
of the uterine mucosa. In the instances observed, the presence 
of maternal blood with many phagocytic leucocytes was noted 
in the lumen of the uterus, adhering to and surrounding the ova. 
From the study of sections of the uteri of an appreciable number 
of albino rats, in which insemination and supposedly semination 
seemed normal, but in which on complete serial sectioning of the 
uterine tubes no ova were found, but in the lumen of the uterine 
tubes of which the presence of maternal blood and phagocytic 
leucocytes was noted, the conclusion seems warranted that 
death and complete absorption of ova, after a given stage of nor- 
mal development has been reached, may occur. In such eases, 
one may with propriety speak of faulty implantation, due to 
altered or pathologic condition of the uterine mucosa, even in 
cases where no actual implantation would have occurred in cor- 
responding normal stages. In the two rats (Nos. 91 and 104) 
in which this condition was observed, the decidual crypts were 
shallow and not developed to the extent normal for the respec- 
tive stages, evidencing the abnormal condition of the mucosa. 
In cases in which a single abnormal or pathologic ovum is 
found in the uterus along with several normal ova, the pre- 
sumption seems justified that the underlying cause responsible 
for the abnormal development is to be sought in the ovum itself, 
and not in its environs. 
Abnormal developmental stages, interpreted as due to irregu- 
lar or retarded segmentation, irregular or abnormal segmenta- 
tion cavity formation, and retarded development of the ecto- 
dermal node and primary embryonic ectoderm, where only a 
single ovum shows abnormal development in a uterus contain- 
ing the average number of ova presenting normal development, 
are difficult to explain on the assumption that extraneous in- 
fluences affecting a single ovum are operative. Practically all 
