810 THE POPULAR SCIENCE MONTHLY. 



eye answers to this description as being a very early organ.* But 

 waiving possible interpretations, let us admit that here is a diffi- 

 culty — a difficulty like countless others which the phenomena of 

 evolution present, as, for instance, the acquirement of such a 

 habit as that of the Vanessa larva, hanging itself up by the tail 

 and then changing into a chrysalis which usurps its place — a diffi- 

 culty which, along with multitudes, has to await future solution, 

 if any can be found. Let it be granted, I say, that here is a seri- 

 ous obstacle in the way of the hypothesis ; and now let us turn to 

 the alternative hypothesis, and observe whether it is not met by 

 difficulties which are much more serious. Weismann writes : 



" The caverns in Carniola and Carinthia, in which the hlind Proteus and so 

 many other blind animals live, belong geologically to the Jurassic formation; and 

 although we do not exactly know when, for example, the Proteus first entered 

 them, the low organization of this amphibian certainly indicates that it has been 

 sheltered there for a very long period of time, and that thousands of generations 

 of this species have succeeded one another in the caves. 



" llence there is no reason to wonder at the extent to which the degeneration 

 of the eye has been already carried in the Proteus, even if we assume that it is 

 merely due to the cessation of the conserving influence of natural selection. 



u But it is unnecessary to depend upon this assumption alone, for when a use- 

 less organ degenerates, tliere are also other factors which demand consideration — 

 namely, the higher development of other organs which compensate for the loss of 

 the degenerating structure, or the increase in size of adjacent parts. If these 

 newer developments are of advantage to the species, they finally come to take 

 the place of the organ which natural selection has failed to preserve at its point 

 of highest perfection." t 



On these paragraphs let me first remark that one cause is mul- 

 tiplied into two. The cause is stated in the abstract, and it is 

 then re-stated in the concrete, as though it were another cause. 

 Manifestly, if by decrease of the eye an economy of nutriment is 

 achieved, it is implied that the economized nutriment is turned 

 to some advantageous purpose or other ; and to specify that the 

 nutriment is used for the further development of compensat- 

 ing organs, simply changes the indefinite statement of advan- 

 tage into a definite statement of advantage. There are not two 



* While the proof of this article is in hand, I learn that the Proteus is not quite blind, 

 and that its eyes have a use. It seems that when the underground streams it inhabits are 

 unusually swollen, some individuals of the species are carried out of the caverns into the 

 open (being then sometimes captured). It is also said that the creature shuns the light ; this 

 trait being, I presume, observed when it is in captivity. Now obviously, among individuals 

 carried out into the open, those which remain visible are apt to be carried off by enemies ; 

 whereas, those which, appreciating the difference between light and darkness, shelter them- 

 selves in dark places, survive. Hence the tendency of natural selection is to prevent the 

 decrease of the eyes beyond that point at which they can distinguish between light and dark- 

 ness. Thus the apparent anomaly is explained. 



\ Essays upon Heredity, p. 87. 



