620 JOHN BEARD, 



At the close of an admirable review of recent progress in our 

 knowledge of the morphology and development of the "germ- organs" 

 or "sexual glands" of Vertebrates, Gustav Born writes as follows: 

 'The methods as yet employed are, as already insisted upon in the 

 introduction, not such as to enable investigators adequately to cope 

 with the problems of this specially difficult domain" ('95, p. 616). 



In thus summing up Born had in view problems dealing, not only 

 with the origin of the "germ-organs" themselves, but also with their 

 subsequent history and connections with other structures. 



But, confining our attention to the one problem of the develop- 

 mental origin of the germ-cells in the Vertebrata, a survey of the 

 researches of the last three decades will furnish ample conviction of 

 the unsatisfactory condition of our knowledge. 



The earliest view to be noted is also that most widely accepted 

 and generally taught. It pervades our text-books, and it has in- 

 fluenced research. In my own note-book, only a few pages before 

 notes of work on the germ-cells begin, there stands a reference to 

 the doctrine of germ-cell origin about to be mentioned, and an at- 

 tempt to use it in framing a theory of the morphological nature of 



the thymus. 



It is now almost 30 years since Waldeyer ('71) set up the doc- 

 trine of the origin of the germ-cells from a specialised portion of the 

 peritoneum. This doctrine has survived all direct or indirect attempts 

 to dethrone it. It is so simple ; and, apparently, so well founded in 

 fact, capable of so ready and easy confirmation withal in the com- 

 monest and most accessible Vertebrate embryos, that its position has 

 seemed secure almost without such confirmatory researches, and m 

 spite of results directly at variance with it. 



If germ-cells arise from certain epithelial cells, as Waldeyer 

 and others have maintained, nothing ought to be easier than to find 

 and exhibit the transitional cells, demonstrating the passage of the 

 one element into the other. One author at least, Semon ('87) in his 

 work on the testis of the chick, distinctly states, that in the strip of 

 modified peritoneum from which this arises, there exist at certain phases 

 all possible transitions from ordinary elongated peritoneal cells to the 

 so-called "primitive ova" or germ cells i). 



1) In the chick the writer has been unable to find any such. 

 But in this animal the germ-cells are in evidence long before there 

 is any "germinal ridge". The like find has also been made by Nuss- 



BAUM ('01). 



