THE ULTIMATE SEX-ET.EMENTS. 95 



appear late. After the differentiation of the vertebrate embryo 

 has progressed far, or the Hfe of the polyps continued for long, 

 the germ-cells make their appearance ; and though we know 

 of course that they are descendants of the original ovum, yet 

 we must allow, with Weismann, that in the form of special cells 

 they are now for the first time to be detected. Therefore, 

 Weismann says, "a continuity of Qerm-re/Zs is now for the most 

 part no longer demonstrable." 



Yet there is nothing that Weismann more strongly insists 

 upon, than the reality of continuity between ovum and ovum. 

 In what does it consist, if a chain of ovum-like cells is only 

 true of a minority of organisms ? It consists, according to 

 Weismann, in the " Keimplasma " or germ-protoplasm. 



The germ-plasma is the distinctive part of the nucleus of the 

 germ-cell. It has an extremely complex, and at the same time 

 persistent, structure. It is the substance which enables the 

 germ-cell to build up an organism, the architectural living 

 matter, and the immortal bearer of all properties transmitted in 

 inheritance. " In every development," according to Weismann, 

 "a portion of this specific germ-i)lasma, which the parental 

 ovum contains, is unused in the upbuilding of the offspring's 

 body, and is reserved unchanged to form the germ-cells of the 

 next generation. . . . The germ-cells no longer appear as 

 products of the body, at least not in their most essential part — the 

 specific germ-plasma ; they appear rather as something opposed 

 to the sum-total of body-cells ; and the germ-cells of successive 

 generations are related to one another like generations of Pro- 

 tozoa." But the continuity is rarely kei)t up by a chain of 

 undifferentiated reproductive ce//s ; it depends upon the con- 

 tinuance and unchanged persistence of a minimal quantity of 

 the original germ-plasma. 



