718 THE GENERATIVE ORGANS. 
amceboid cells, which wander through the yelk to its periphery 
and there again unite and form the blastoderm. 
The improbability of such a theory is so great that it would 
require far stronger evidence than has yet been adduced to 
make it acceptable. No other instance occurs in nature of an 
embryo originating from numerous wander-cells, or parablastic 
elements. Moreover there is nothing to show that the germ- 
yelk does not form a continuous blastoderm by its segmenta- 
tion, just as it does in other animals. 
If no such cell as the germ-cell can be found in the yelks 
whilst still in the ovary—since it is highly improbable that such 
a cell is formed around a nucleus, which in the first instance is 
the nucleus of a yelk-cell—such a germ-ovum must have a 
separate origin and must enter the egg from without, during 
its passage through the oviduct. 
It is true that in the egg of a bird the yelk consists chiefly of 
food material, in which the germ-cell is included, but the whole 
developmental history of the bird’s egg is different, and no one 
doubts the existence of the germ-yelk at an early period of 
development as a well-marked structure. I admit that if the 
ova of insects could be shown to consist at first of a single cell, 
that the above argument would be less valid, but even then the 
changes which the nucleus undergoes would not permit it to 
be compared with a germinal vesicle—the degeneration is 
marked, and all the details of the process resemble those which 
occur in degenerating nuclei. 
i. On the Development of the Germ-Ova in the Epithelial Cells of 
the Parovarium. 
In the earlier stages of development the parovarium is lined 
with a distinct layer of large epithelial cells, and this condition 
persists for a long time in the anterior or blind end of the 
gland. In many of my sections the epithelial lining of the 
gland appears as a continuous layer of protoplasm, in which 
numerous nuclei are embedded. So that in this respect 
