568 Gideon S. Dodds. 



process. Moreover it is to be noted that several recent investi- 

 gators who have made careful search, have been entirely unable 

 to find any indication that, there is such a transform ation and em- 

 phatically state that germ-cells are not produced in this way. 



Probably the circumstance which contributed much to the 

 belief in a germinal epithelium was the inability of investigators 

 to recognize the germ-cells in earlier stages. This failure of many 

 observers is not to be wondered at, because in the early stages the 

 germ-cells are very obscure, and become easily found and recog- 

 nized only when they reach the peritoneum in the position of the 

 genital ridge. 



Of recent years, however, many investigators of vertebrate 

 embryos have been able actually to show that the peritoneum is 

 not the place of origin of the primordial ova and have clearly 

 traced them in the earlier stages, while they are migrating to the 

 peritoneum covering the genital ridge. Such clear positive evi- 

 dence of an early origin renders worthless the doubtful evidence 

 for a peritoneal origin. In every group of vertebrates, except 

 the mammals where the problem is more difficult, the germ-cells 

 have been clearly recognized before they have reached the genital 

 ridge and in several forms they have been traced back to the be- 

 ginning of embryo formation. 



With regard to the gonotome theory there seems little to be 

 said. It was never widely accepted and all the recent evidence 

 is against it. The conditions observed by Riickert and Van 

 Wijhe are capable of other interpretation and would probably 

 be other\^ise explained by those men themselves in the light 

 of more recent discoveries. One recent paper of importance 

 describing a segmental origin of the germ-cells is that of Dustin 

 ('07) on Amphibia. The observations recorded in this paper are 

 so directly contrary to the accounts of other recent works on this 

 group that we are not justified in accepting his view without fur- 

 ther evidence. 



The above views of the origin of the germ-cells in vertebrates 

 are mutually exclusive. The tracing of the gem. -cells to an ori- 

 gin in prin:itive tissue of the ear'y enxtryo, disproves both views 



