468 CHARLES H. SWIFT 



In the cortical masses or cords there are, as formerly described, 

 two kinds of cells — the oogonia and the follicular cells (fig. 8). 



The further history of the oogonia in the chick has been ad- 

 mirably presented by d'Hollander ('04) and Sonnenbrodt ('08), 

 who have described in detail the changes, nuclear and otherwise, 

 which the oogonia and oocytes undergo in the process of oogenesis. 

 The reader is referred to their accounts for the details of the 

 processes which transform the oogonium into the ovum and 

 some of the deep indifferent cells into the follicular epithelium. 



SUMMARY AND CONCLUSIONS 



1. During the two days subsequent to the development of the 

 germinal epithelium, which occurs between the 80th and 90th 

 hours of incubation, a majority of the primordial germ-cells are 

 found between the cells of that tissue. Some of the remaining 

 primordial germ-cells are present in the mesenchyme beneath 

 the germinal epithelium, others are found in the cords of uro- 

 genital union, while still others remain in the root of the mesen- 

 tery. The latter may be seen in that situation in some embryos 

 until the 9th day of development, when they degenerate. 



During the 4th and 5th days of development it is possible to 

 count, with a considerable degree of accuracy, the germ-cells 

 in the gonads, and if that is done, it will be found that the number 

 on the left side exceeds that of the right in the proportion of 2 

 to 5 to 1. 



2. During the Gth and 7th days of development the germinal 

 epithelium sends down into the subjacent tissue a first series of 

 sexual cords or cords of first proliferation. These cords are pro- 

 duced as a result of localized activity of the germinal epithelium. 

 The cords of first proliferation are epithelial in character, and the 

 germ-cells, which are present in them, apparently have nothing 

 to do with their formation, however, it is not beyond a possibility 

 that certain of the germ-cells play a metabolic role in stimulating 

 the epithelial cells around them to activity. 



The cords of first proliferation in the male .become the semen- 

 iferous tubules and in the female the medullary cords. 



