THE DEVELOPMENT OF TH! MOLE. 161 
with regard to the early phases of development, throw some 
light upon the curious differences wh’ch then occur. 
Kolliker (No. 14, 2nd edit., p. 44) and Schulin (No. 20), 
declare that the human ovum is markedly deficient in yolk 
vesicles when compared with the ovum of the Cat or the Cow. 
Bischoff (Nos. 8, 9, 10, 11), in his figures of the ova of 
the Rabbit, Dog, Guinea-Pig and Deer, shows that the 
Deer’s ovum is not filled with such a dense mass of yolk as is 
that either of the Dog or Rabbit, while the ovum of the 
Guinea-Pig is remarkably transparent, a statement in the 
latter case with which Reichert’s (No. 18) and my own obser- 
vations fully coincide (vide fig. 21). The Mole’s ovum must 
be classed in this particular with that of the Rabbit and Dog, 
while the Bat’s ovum it appears is similar to that of the 
Guinea-Pig. 
The network, which has as far as I know hitherto only been 
observed in Mammalian ova by Schafer (No. 19) in young 
ovarian ova of the Rabbit, was very distinct in the ovum repre- 
sented in fig. 2. A similar appearance was noted in other 
ova, but in a considerable number no such network could be 
detected. There appears to me, however, good reason to 
believe that the appearance is due to a protoplasmic reticulum 
in the meshes of which the food material lies. 
Tuer NvcLevs. 
In all those ova in which the nucleus was observed it was 
placed excentrically ; the density of the yolk being so great 
it could not be distinguished when lying in the centre of the 
ovum. It was found to be either circular or oval in optical 
section, and bounded by a distinct membrane. In the ovum 
represented in fig. 2, the nucleus is indicated by a circular ring ; 
its contents could not, however, be observed owing to the density 
of the supervening yolk, the network before spoken of being 
seen overlying the nucleus. 
In figs. 3,4, 5, 1 have drawn the nuclei of three ova which 
I obtained from the female from which the ovum drawn in 
