400 POPULAR SCIENCE MONTHLY. 



Kohl* considers that "Der Grund und direkter oder indirekter Anlass 

 zum Eintreten der Entivickelungslicmmung ist Lichtmangel." The 

 method of operation of the lack of light he conceived to be as follows: 



Other organs were developed to compensate for the disuse of the 

 eye; and as the developmental force was used in the formation of these 

 organs, each succeeding generation developed its eye less. The de- 

 generation is thus explained as the result of a struggle of parts, 

 although this term is nowhere used, acting through the principle of 

 compensation. The same objections may be offered to this explana- 

 tion of Kohl as to all his theoretical discussions — they are based on the 

 assumption of conditions and processes that have no existence. The 

 high development of 'compensating 5 organs is not primarily the result of 

 the loss of the eye, but the high development of the former organs per- 

 mitted the disuse and later degeneration of the latter. His whole 

 process is a phylogenetic one, without a preceding ontogenetic one, 

 though on this point he does not seem to be very clear himself, for on 

 one page we are told that degeneration leads to retardation, and on an- 

 other that degeneration is a consequence of retardation. 



Ledenf eldt endeavors to apply Roux's Kampf der Theile, with re- 

 versed selection, to explain the conclusions reached by Kohl on the 

 processes and causes of degeneration. The struggle is represented as 

 taking place between the germ and soma, the former endeavoring to 

 keep the latter at the lowest efficient point as weapon for the germ. If a 

 series of individuals get into the dark the organs of vision are of no 

 advantage and reversed selection will bring about their degeneration. 

 The saving in ontogeny appears first as a retardation and then as a ces- 

 sation of development. 



Weismannt more recently accepts the view of Romanes, Morgan and 

 Lankester on the inadequacy of panmixia to explain the whole phe- 

 nomena of degeneration, and in his 'Germinal Selection' rejects the idea 

 of reversed selection, and suggests a new explanation for what Romanes 

 attributed to the failure of heredity and the Lamarckians to transmis- 

 sion of the effects of disuse. The struggle of the parts of Roux has been 

 crowded by him back to the representatives of these parts in the germ. 



"The phenomena observed in the stunting, or degeneration, of parts 

 rendered useless . . . show distinctly that ordinary selection, 

 which operates by the removal of entire persons — personal selection, as 

 I prefer to call it — can not be the only cause of degeneration, for in 

 most cases of degeneration it can not be assumed that slight individual 

 vacillations in the size of the organ in question have possessed selective 

 value. On the contrary, we see such retrogressions effected apparently 



* Rudimentare Wirbelthieraugen, 1893. f Zoologischer Central blatt, 1896. 



t The Monist, 1896, pp. 260-274. 



