52 An Examination of Weismannism. 



meet them? As we have already seen in Chapter II, 

 he meets them in the only way they can be met on 

 the lines of his theory — viz.. by those newer amend- 

 ments of his theory which suppose that in all these 

 cases the germ-plasm is not confined to the specially 

 sexual cells, but occurs also in the nuclear substance 

 of those somatic-cells which thus prove themselves 

 capable of developing into entire organisms. In 

 other words, the sexual elements which develop 

 during what I have previously called this "'somatic 

 reproduction " of multicellular organism, are supposed 

 to be derived from the sexual cells of ancestors, not 

 indeed immediately (for this they plainly are not), 

 but mediately through the somatic-tissues of their 

 a-sexual parent. Now, in view of this extension, the 

 theory of germ -plasm becomes somewhat closely 

 allied to that of pangenesis. For example, when the 

 fragment of a leaf of Begonia is laid upon moist soil, 

 there strikes root, and grows a new Begonia plant 

 capable of sexual reproduction Darwin supposes the 

 explanation to be that what he calls " formative 

 material" occurs in all cells of the leaf, while Weismann 

 supposes the explanation to be that what he calls 

 " germ-plasm " occurs in all — or at any rate in most — 

 of the cells of the leaf. So that, except as regards the 

 terms employed, the two theories are identical in their 

 mode of viewing this particular class of phenomena. 



Moreover by thus allowing, in his second essay on 

 Heredity, that germ-plasm need not be restricted to 

 the specially sexual cells but in some cases, at any 

 rate 1 , may occur distributed in full measure of repro- 



1 We have no means of estimating exactly the proportional number 

 of cases in -which this is possible, either among the lower or the higher 



