1896.] ^C)6 [Ortmami. 



without a cbange or differentiation of external conditions of life : then a 

 differentiation of species does not result, but we shall have the same spe- 

 cies in separated localities. We call such species " relicts" from a former 

 continuous distribution.* 



Eiraer, although he appreciates the value of geogi-aphical separation, 

 names other causes besides: but what he calls " genepistasis " and 

 " kyesamechania " are nothing else than particular actions of separation. 



But for a plain understanding we should examine Elmer's theories more 

 closely. f 



Eimer:}: defends the opinion that variations are caused by external con- 

 ditions, but that variability is not an indefinite one, but that the varia- 

 tions are comparatively few, and take place only in distinct directions. 

 There is, according to him, no "fortuitous" or "irregular" variability, but 

 a variability in certain few and distinct lines : he calls this the principle of 

 Orthogenesis, and believes that it is contrary to Darwin's alleged supposition 

 of unlimited and " fortuitous " variability. I can hardly see that this differ- 

 ence from Darwin exists at all. It is true Darwin uses the words "indefi- 

 nite variability," but certainly not in the sense as interpreted by Eimer 

 ("zufal'ig," "regellos"). Darwin says ;g " All such changes of struc- 

 ture, whether extremely sliglit or strongly marked, which appear amongst 

 many individuals living together, may be considered as the indefinite 

 effects of the conditions of life on each individual organism, in nearly the 

 same manner as a chill affects different men in an indefinite manner, accord- 

 ing to their state of body constitution," etc. That is certainly not a varia- 

 bility subject to casuality, but a variability governed by external causes, 

 which may differ only according to the disposition of the individuals, and 

 this opinion, that "the nature of the organism and the nature of the con- 

 ditions "|| are connected in the formation of variations, is also upheld by 

 Eimer.^ 



Further, he lays much stress upon the fact that variability advances in 

 a definite direction (orthogenesis), but, I think, he confounds here two 

 actions, that of variation and that of inheritance. Orthogenesis is varia- 

 tion, which is transmitted, and which is accumulated by the repeated 

 action of the same external causes upon a series of descendants. We can 

 hardly decide, whether a variation lends to advance in a distinct direction, 

 unless we see that again and again specimens vary in the same direction, 



*Grundzilge, etc., p. 34 and p. 86. 



+ 1 go more iuto details here than seems perhaps necessary, because I consider Elmer's 

 investigations as very important, especially as regards the facts collected. But we shall see 

 that Elmer's views do not differ considerably from Darwin's, and that the chief differences 

 are ouly differences of terminology. 



X Eimer, Die Entstehung der Arten aiif Grund von Vererbung erworhener Eigensehaflen naeh 

 den Gesetzen organischen Wachsens, i, 1888. 



§ Origin of Species, p. 6. 



\\ Ibid., p. 6. 



yComp. I. c, p. 5. Variation is effected by " Weehselwirkung zwisohen der stofflichen 

 Zusammensetzung des Korpers und iiusseren Einfliissen." 



