238 BLIND VERTEBRATES AND THEIR EYES. 



was never very extensive. Much more potent in placing the eye in harmony with 

 its environment was the fact that every succeeding generation developed its eye less. 

 This process of Hemmung of the eye did not begin until the developmental force 

 began to go to the development of the compensating organs. On account of the 

 loss of this developmental force the eye was unable to reach, in successive genera- 

 tions, the former grade. The degeneration is thus explained as the result of a 

 struggle of parts, although this term is nowhere used, acting through the princi- 

 ple of compensation. The same objections may be offered to this explanation 

 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 " organs is not primarily the result of the loss of the eye, but the 

 high development of the former organs permitted the disuse and later degeneration 

 of the later. His whole process is a phylogenetic one without a preceding onto- 

 genetic 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 another that 

 degeneration is a consequence of retardation. 



Lendenfeld endeavors to apply Roux's Kampf der Theile with reversed selec- 

 tion to explain the conclusions reached by Kohl on the processes and causes of 

 degeneration. The struggle is represented to take 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 gets into the dark, the organs of 

 vision are of no advantage, and reversed selection will bring about their degenera- 

 tion. The saving in ontogeny appears first as a retardation and then a cessation 

 of development. 



Weismann later accepted the view of Romanes, Morgan, and Lankester of 

 the inadequacy of panmixia to explain the whole phenomena 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 disuse transmission. The struggle of the parts, of Roux, has 

 been crowded back by him 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 has possessed selective 

 value. On the contrary, we see such retrogressions affected apparently in the 

 shape of a continuous evolutionary process determined by internal causes, in the 

 case of which there can be no question whatever of selection of persons or of a 

 survival of the fittest, that is of individuals with the smallest rudiments." The 

 gradual diminution, continuing for thousands and thousands of years and cul- 

 minating in its final and absolute effacement, can only be accomplished bv ger- 

 minal selection. Germinal selection as applied to degeneration is the formal 

 explanation of Romanes' failure of the hereditary force and the establishment of 

 disuse effects in the heredity through the struggle of parts for food. "Powerful 

 determinants will absorb nutriment more rapidly than weaker determinants. The 

 latter, accordingly, will grow more slowly and will produce weaker determinants 

 than the former." If an organ is rendered useless, the size of this organ is no longer 



