158 The Science of Life. 



are still awanting, the matter lies beyond the scope of 

 this historical sketch. 



(2) Virchow has urged against Weismann what ap- 

 pear to him to be cases of the direct inheritance of 

 climatic changes and pathological variations. But he 

 appears to differ from Weismann in his definition of 

 acquired characters, which, for the latter, do not include 

 anything that can reasonably be traced back to a 

 germinal variation. Ziegler has discussed the whole 

 question of the inheritance of pathological characters, 

 and comes to a conclusion harmonious with that of 

 Weismann. Nor are the slow results of acclimatization 

 good cases in the present discussion, since Weismann 

 expressly allows that in long- continued conditions 

 affecting the whole system the germinal cells may be 

 directly affected along with, though not exactly by, the 

 other elements of the organism. 



(3) A criticism of a different nature has been sug- 

 gested by several, but is well stated by Eimer. If the 

 source of variation be restricted by hypothesis to the 

 keimplasma intermingled in sexual reproduction, is this 

 sufficient to account for the facts? " In what way, one 

 must ask, have new characters first been introduced 

 into the series? The sexual mixture could produce 

 nothing; it could only work with what was already 

 given." Professor M'Kendrick has forcibly emphasized 

 a similar objection. There is no doubt, at any rate, 

 that Weismann's theory, which excludes the direct 

 assistance of environmental and functional variations, 

 throws a still heavier burden than Darwin did on the 

 shoulders of Natural Selection, which many believe to 

 be already somewhat overweighted. 



At the same time, it seems premature to conclude 

 that the transmission of modifications is impossible, 

 simply because we can find no proof of it, nor under- 

 stand how it could be effected. In this connection it 

 may be useful to recall a few general facts. 



Every one allows the general conception of the various 

 organs as symbions in a common life. We constantly 

 speak of correlated variations, and though these gener- 

 ally work from the centre or germinal plasma outwards, 



