94 



THE EVOLUTION OP^ SEX. 



■'({ 



A 



developed part of the stirp is almost sterile " (i.e., without in- 

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

 velo{)ed 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-])rotoplasm. 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. IVeismann^s Theory of the Continuity 

 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 

 l)etween 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 authors quoted have si)oken of the con- 

 tinuity of the germ-ri7A\ This is certainly 

 true for some cases. If it were true for all, 



cession of Protozoa; |-}-,^ problems of rcproductiou and heredity 



lurttier on, It represents 111 1 • i 1 



the ova from which the would bc much smiplcr than they at present 



"bodies" (undotted) ^^^r^pT,- f^ l.p 

 are produced. At each •^q^P^''^^ ^O Oe. 



generation, a sperma- For in the prcscnt statc of our know- 



tozoon fertilisintr the 1 i i \ r .\ .-• . 



liberated ovum is also l^dgc wc can Only spcak ot tlic Continuity 



indicated. Qf ^^^ rcproductivc cclls., \\\ cxccptiona" 



rather in a small minority of cases. Alike in the 



brates and the lowly hydroids, the reproductive cells may 



The relation between re- 

 productive cells and the 

 body. The continuous 

 chain of dotted cells at 

 first represents a suc- 



or 

 higher verte- 



