7 i8 THE GENERATIVE ORGANS. 



amoeboid 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 



