﻿240 BLESro VERTEBRATES AND THEIR EYES. 



Weismann attempts to explain the degeneration beyond the point which pan- 

 mixia can reach by a process which not only is insufficient, if all his premises are 

 granted, to produce the desired result without the help of use transmission, but 

 has as its result a horizontal degeneration which does not occur in the eyes. 



Romanes supposed degeneration, beyond the point which may be reached by 

 panmixia, to be the result of personal selection and the failure of the hereditary 

 force. The former is not applicable to the species in question and is denied by 

 such an ardent Darwinian as Weismann to be applicable at all in accounting for 

 degeneration. Moreover the process as explained by Romanes would result in a 

 horizontal degeneration which has no existence in fact. The second assumption, 

 the failure of hereditary force, is not distinguishable, as Morgan has pointed out, 

 from the effect of use transmission. 



The struggle of parts in the organism has not affected the eye through the lack 

 of room, since the space formerly occupied by the eye is now filled by fat and not 

 by an actively functioning organ. It is not affected by the struggle for food, for 

 stored food occupies the former eye space. It could only be affected by the more 

 active selection of specific parts of food by some actively functioning organ. It is 

 possible that this has in fact affected the degeneration of the eye. The theory 

 explains degeneration in the individual and implies that the effect in the individual 

 should be transmitted to the next generation. This second fact seems but the 

 explanation of the working of the Lamarckian factor. 



Mutation can produce definitely directed evolution such as we find in the 

 degenerating eye only when each step, each successive mutation, has an advantage 

 over the mother or sister lines. I do not think that any one after familiarizing 

 himself with the variation of the eye and its insignificance will maintain that this 

 minute organ is now or has been for many generations of selective value. If it is 

 not of selective value, mutation is as powerless to account for its condition as is 

 natural selection of favorable variations. 



The eyes of the two sides vary so much, independent of each other, that we 

 are forced to conclude that there has been no check on their variation for a long 

 period. 



The only answer to the objection that the eyes are not the result of personal 

 selection is that they may be so correlated with another organ inversely propor- 

 tionate to it, that the selection of individuals with this other organ in favorable 

 condition carries with it the selection of individuals with the eye in decreasingly 

 imperfect condition. No such organ is available. 



The Lamarckian view, that through disuse the organ is diminished during the 

 life of the individual, in part at least on account of the diminution of the amount 

 of blood going to a resting organ, and that this effect is transmitted to succeeding 

 generations, not only would theoretically account for unlimited progressive degenera- 

 tion, but is the only view so far examined that does not on the face of it present 

 serious objections. Is this theory applicable in detail to the conditions found in 

 the Amblyopsidte ? Before going farther, objections may be raised against the 

 universal assumption that the cessation of use and the consequent panmixia was a 

 sudden process. This assumes that the caves were peopled by a catastrophe. But 

 it is absolutely certain that the caves were not so peopled, that the cessation of 

 use was gradual and the cessation of selection must also have been a gradual pro- 



