The germ-cells. 693 



vations, those of Nussbaum and Eigenmann excepted, are very frag- 

 mentary 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 oc- 

 currence 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 = Micro- 

 metrus. 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. 



XVIII. The morphological Continuity of Grerm-Cells. 



Nussbaum's conclusion was enunciated at least twenty years too 

 soon. It deserves a place of honour much higher than it has hitherto 

 occupied. Perhaps now, after we have witnessed the work and writings 

 of Weismann, the results of the researches of Boveri, Hacker, 

 0. Hertwig, Rückert and Spemann — to name only a few of the 

 most prominent workers in this field — the absurdity of Nussbaum's 

 conclusion may not be so palpable. 



For myself, in reviewing the actual facts of my observations, I 

 most emphatically endorse the correctness of his brilliant idea. There 

 is no real evidence, showing that germ-cells are ever formed from 

 any part of the embryo. If no part of the embryo be used up in 

 forming them, though in it, they are not of it. In the skate they 

 are formed long before there is any embryo at all. As already in- 



