THE MIGRATION OF THE PRIMARY SEX-CELLS OF 

 FUNDULUS HETEROCLITUS. 



A. RICHARDS AND JAMES T. THOMPSON, 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF OKLAHOMA. 



The origin of the primary sex-cells in vertebrates is a problem 

 which has received considerable attention during late years. Ex- 

 tensive summaries of the literature upon this subject may be 

 found in the articles of Allen, 1911, and Jordan, 1917. Since no 

 complete agreement with regard to details has as yet been reached, 

 it is perhaps desirable to review briefly the earlier investigations, 

 and to point out any discrepancies in the results already obtained 

 which would seem to require further study. It would seem that 

 more evidence is necessary to warrant safe conclusions on the 

 matter. 



Waldeyer (18/0) first described the differentiation of the sex- 

 cells from the " germinal epithelium " of a four-day chick. His 

 view of sex-cell origin from the mesothelium covering the meso- 

 nephros was accepted at the time, and has been supported even by 

 recent investigators. In 1880 Nussbaum advanced a rival theory 

 as a result of his observations on the embryology of the trout and 

 frog. He held that the sex-cells were of blastomeric origin, and 

 further that there was an extra-regional segregation and a migra- 

 tion to the germ gland. Weismann (1886) popularized this idea 

 in his work on the " continuity of the germ plasm." 



Since the time of Nussbaum the evidence against the " germinal 

 epithelium" idea has steadily increased. A number of investi- 

 gators (Hoffman, 1892; Eigenmann, 1892; Beard, 1900; Woods, 

 1902; Allen, 1906, 1907, 1911; Dodds, 1910; Swift, 1914, 1915, 

 1916; Jordan, 1917) have failed to find any conditions not in ac- 

 cord with Nussbaum's theory. 



However other recent workers (Firket, 1914, 1920; von Beren- 

 berg-Gossler, 1914) have been unable to accept this interpretation 

 of the activities of these cells. According to their viewpoint, the 



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