484 



The Morphological Continuity of Germ-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 writ- 

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

 Spemann, and Rückert — 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 they be in it, they are not of it. In the skate they are 

 formed long before there is any embryo at all. As already insisted, 

 each germ-cell is the sister-cell of the cell destined to give rise to 

 the embryo. If one of them were to begin development alongside 

 of the developing embryo, the result would be the production of a 

 more or less perfect twin. This is practically what happens in the 

 growth of a dermoid in the ovary, testis, or elsewhere. In such ab- 

 normal cases, the embryomas of Wilms, the embryoma, if it became 

 a fully developed individual, would be the sister of the form, in which 

 it arose, and not its offspring. 



The germ-cells of like generation with the embryo, or primary 

 ones, are destined for future generations; and before they, or any of 

 them, develop and form normal embryos, they undergo many divisions, 

 forming secondary germ-cells: and, finally, these pass through the 

 processes we term ripening, etc. In undergoing these divisions they 

 cease to be of the same generation as the form, which harbours them, 

 and they become members of a morphologically different and younger 

 generation. 



The term "of the like generation" here employed may be objected 

 to as a misnomer. That is a disadvantage, which it shares with the 

 name germ-cell or "Keimzelle" of German authors. Keimzellen accord- 

 ing to His are certain cells of the developing nervous system. The 

 same name is applied by Rückert to cells of the segmentation, not 

 identified as the future "sexual cells". 



In Raja batis the germ-cells and the original embryonic cell are 

 in the strictest sense of the like generation up to a certain point. At 

 this, the parting of the ways, the comparison ceases. The cell, destined 

 to form the embryo, parts company from the germ-cells, which for 

 a while remain in a resting phase. It is from this point, that the 



