GERM-CELL ORIGIN 



115 



matin materials, is not tenable for experimental and cytological evidence sug- 

 gests that all cells of the body contain the same chromosomal materials. 

 However, it should be pointed out that Weismann was one of the first to 

 suggest that the chromosome complex of the nucleus acts as a repository 

 for all of the hereditary characteristics of the species. This suggestion relative 

 to the role of the nucleus has proved to be one of the main contributions to 

 biological theory in modern times. 



Fig. 60. Representation of the concept of the early embryonic origin of the primordial 

 germ cells and their migration into tiie site of the developing germ gland. (A-C are 

 adapted from the work of Allen, Anat. Anz. 29, on germ cell origin in Chrysemys; D-F 

 are diagrams based on the works of Dustin, Swift, and Dantschakoff, etc., referred to 

 in the table of germ-ceil origins included in the text.) (A-C) Germ cells arising within 

 the primitive entoderm and migrating through the dorsal mesentery to the site of the 

 primitive gonad, shown in (D), where they become associated in or near the germinal 

 epithelium overlying the internal mesenchyme of the gonad. (E, F) Increase of the 

 primitive gonia within the developing germ gland, with a subsequent migration into the 

 substance of the germ gland of many germ cells during the differentiation of sex. 



