483 



late phases; and, therefore, it may be said of them, that they prove 

 nothing whatever as to the first origin of the germ-cells. 



The researches of Nussbaum, Hoffmann, Prenant, Eigenmann, 

 and Wheeler all go to disprove any genetic relationship between 

 the germinal epithelium and the "primitive ova" or germ-cells. 



In his recent contribution to the subject Rabl ('96) never refers 

 to either of the above views; but from the circumstance, that he 

 traces back the first germ-cells to embryos of 18 somites, and hints 

 that the possibility of an even earlier occurrence cannot be excluded, 

 his researches furnish no support to the epithelial view, and point, 

 in fact, in the other direction. 



The researches of Nussbaum and others, so far as they go, all 

 favour an origin of germ-cells independently of the tissues of the 

 embryo; or, at any rate, they lend no support to a relationship with 

 any particular tissue or group of cells. Unfortunately, except those 

 of NUSSBAUM and Eigenmann, these observations are very fragmentary 

 in character, and they tell very little. 



Hoffmann has seen and correctly interpreted vagrant germ-cells 

 in the mesoderm of the mesenterial root. Prenant records their 

 occurrence on parts of the peritoneum adjacent to the germinal epi- 

 thelium. Wheeler ('99) finds the germ-cells of the lamprey to be 

 represented at a very early period by a few large cells, situated at 

 the junction of mesoblast and hypoblast. 



Of all these authors the one, whose results bear most resemblance 

 to mine, is Eigenmann ('92). His original observations are also de- 

 scribed in two subsequent works without any further new facts as 

 to the first origin of the germ- cells in the Teleost, Cymatogaster 

 == Micrometrus. The number of the original germ- cells, found before 

 any protovertebrae were present, and surmised to have been derived 

 from a very early period of the egg-cleavage, the fifth division, is very 

 limited, being from 9 to 23. These remain constant for a very long 

 time, except that two of them in the gill-region and two others near 

 the middle of the body "are lost" : that is, they probably degenerate. 

 In his record of their presence far forward in the embryo, the dis- 

 appearance of some of them, their migrations, and their very early 

 origin Eigenmann's researches are in agreement with mine. Curiously 

 enough, although he relegates their origin to an early period of the 

 cleavage, he repudiates as absurd Nussbaum's view, that the "sex- 

 cells" are special cells of the segmentation-period, which take no share 

 at any time in building up the individual. 



31* 



