94 



THE EVOLUTION OF SEX. 



developed part of the stirp is almost sterile " (/.^., without in- 

 fluence in heredity); "it is from the unde- 

 veloped residue that the sexual elements are 

 derived.'' 



(/) Lastly, in 1880, Nussbaum, in an 

 elaborate investigation on the differentiation 

 of the reproductive cells, drew emphatic 

 attention to some cases of their early separa- 

 tion, and reasserted Jager's conception of 

 a continuity of germ-protoplasm. In this 

 survey, however, we do not pretend to decide 

 the difficult question of priority in the 

 enunciation of this conception. Like many 

 other generalisations, it appears to have 

 arisen all but simultaneously in many minds. 

 ,^ 9. Weismann's Theory of the Contmiiity 

 of the Germ- Protoplasm. — In some cases 

 referred to in a foregoing paragraph, it is 

 possible to trace a direct cellular continuity, 

 first of all, between the ovum and early 

 separated reproductive rudiments , secondly, 

 between the latter and the future ova and 

 sperms. There is not only cellular continuity 

 between the ovum which gives rise to parent, 

 and the ovum which gives rise to offspring, 

 — that the cell-theory demands, — but there is 

 a continuity in which the character of the 

 original ovum is never lost by differentia- 

 tion. In fact, there is a continuous chain 

 ° ^ of reproductive cells quite apart from the 



^ body cells. It is in this sense that some of 



The relation between re^ ^j^g authors quotcd havc spoken of the con 



productive cells and ___ 



body. The continuous tinuity of the gQx.xn-cells 



chain of dotted cells at 

 first represents a suc- 



true for some cases. 



This is certainly 

 If it were true for all. 



sion of Protozoa; the probleuis of reproduction and heredity 



iLiither on. It represents i i i i • i i i 



the ova from which the would be uiuch sHiiplcr than they at present 



ces: 

 furth 



^bodies" .(undot^ted) appear to bc. 



For in the present state of our know- 



are produced. At ( 

 generation, a sperma- 



Hbem'Jed^^ovumTs a\so l^dge wc can Only spcak of the continuity 

 indicated. gf the rcproductivc cells^ in exceptional or 



rather in a small minority of cases. Alike in the higher verte- 

 brates and the lowly hydroids, the reproductive cells may 



