694 JOHN BEARD, 



sisted, each germ-cell is the sister-cell of the cell, destined to give 

 rise to the embryo. Up to a certain point they are cells of the like 

 generation with it. Were one of them 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 according 

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

 name is applied by RtiCKERT and His 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, de- 

 stined 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 

 real beginning of the unfolding of the embryo must be taken as 

 dating. It and its cells can no more revert to this starting point 

 than a man can return to his childhood. The life of the individual 

 has been initiated. 



While all this is taking place, the germ-cells have remained pas- 

 sive. If one or other of them come into activity, the result is the 

 abnormal production of a twin, or of a pathological growth or dermoid, 

 an abortive embryo. Anon, the time arrives for the awakening of the 

 primary germ-cells, and for the formation of secondary germ-cells. 

 They begin to increase, but this multiplication is such, that no dif- 

 ferentiations, comparable to those which produced the embryo, result. 

 Instead thereof, a much greater number of secondary germ-cells 



