266 



B, like A, lias both a personal structure and reproductive cells, 

 or germ-plasm, the latter of which is represented by the letters 

 ab, which are intended to show that while belonging to B they 

 have a line of continuity with A. C stands for an individual of 

 the third generation, in which the reproductive plasm is indicated 

 by abc, to express that, thougli within the body of C the germ- 

 plasm is continuous with that of both h and a. 



T> also contains the reproductive cells abed, which are continu- 

 ous with tlie germ-plasm of the three preceding generations, and 

 so on ; or for the sake of clearness to put the matter in yet an- 

 other way as suggested by Dr. Romanes, we might represent the 

 germ-plasm by the metaphor of a yeast-plant, a single particle of 

 which may be put into a vat of nutrient fluid ; there it lives and 

 growls upon the nutriment supplied, so that a new particle maybe 

 taken to impregnate another vat, and so on ad injinitum. Here 

 the successive vats would represent successive generations of 

 progeny. But to make the metaphor complete one would require 

 to suppose that in each case the yeast-cell was required to begin 

 by making its own vat of nutrient material, and that it w^as only 

 the residual portion of the cell which was afterwards able to 

 grow and multiply. But though the metaphor is thus necessarily 

 a clumsy one it may serve to emphasise the all -important feature 

 of Weismann's theory, viz., the almost absolute independence of 

 the germ-plasm. For, just as the properties of the yeast-plant 

 would be in no way affected by anything that might happen to 

 the vat, short of its being broken up or having its malt impaired, 

 so, according to Weismann, the properties of the gecm-plasm can- 

 not be affected by anything that may happen to its containing 

 soma, short of the soma being destroyed or having its nutritive 

 functions impaired. 



The consideration of this theory would be manifestly incom- 

 plete without reference to its modus operandi in the origination 

 of new species, and it has already been stated that it requires 

 the assumption that congenital variations only being inheritable 

 no variation impressed upon the organism by the action of its 

 environment — that is, no acquired variation can be in the S-tme 

 way transmitted. 



Such acquired variations, however advantageous to the indi- 

 vidual, cease with the life of that individual — are intransmisable 

 to succeeding generations, and therefore of no account phylogeneti- 

 cally. Congenital Aariations alone tell in the process of organic 

 evolution, and, remembering the facts we have stated as to the 

 advantage of sexual reproduction in respect of the production of 

 congenital variations, we can see how the process of natural selec- 

 tion has for its base of operations the innumerable congenital 



