CAUSES OF DEGENERATION IN BLIND FISHES. 399 



panmixia in that those born with defects may breed with the others. 

 He supposes that the blind fauna may have arisen in but few or several 

 generations, a supposition that may be applicable to invertebrates, but 

 certainly is not to vertebrates. At first those becoming so modified that 

 they can do without the use of their eyes would greatly preponderate 

 over those 'eongenitally blind.' "So all the while the process of adapta- 

 tion was going on, the antennae and other tactile organs increasing in 

 length and in the delicacy of structures, while the eyes were meanwhile 

 diminishing in strength of vision and their nervous force giving out, 

 after a few generations — perhaps only two or three — the number of 

 congenitally blind would increase, and eventually they would, in their 

 turn, preponderate in numbers." Packard seems here to admit the 

 principle of degeneration as the result of compensation of growth, the 

 nervous force of the eye giving out with the increase of the tactile and 

 olfactory organs. It is somewhat doubtful in what sense the term 

 'congenitally blind' is used, but it probably means born blind as the 

 result of transmitted disuse, rather than blind as the result of fortuitous 

 variation. The effects of disuse are thus supposed, through their trans- 

 mission, to have given rise to generations of blind animals. The con- 

 tinued degeneration is not discussed. 



Romanes maintained that the beginning of degeneration was due to 

 cessation of selection, and continued degeneration to the reversal of 

 selection and final failing of the power of heredity. Selection he 

 supposed to be reversed because the organ no longer of use "is absorbing 

 nutriment, causing weight, occupying space and so on, uselessly. Hence, 

 even if it be not also a source of actual danger, economy of growth will 

 determine a reversal of selection against an organ which is now not only 

 useless, but deleterious." This process will continue until the organ 

 becomes rudimentary and finally disappears. 



Roux* attempted chiefly to explain degeneration in the individual. 

 Degeneration is looked upon as the result of a struggle among the parts 

 for (a) room and (6) food. Without doubting that both these principles 

 are active agents in degeneration, it may be seriously doubted whether 

 they are effective in the degeneration of the eyes in question. Certainly 

 there can be no question of a struggle for room, for the position and 

 room formerly occupied by the eye is now filled with fat, which can not 

 have been operative against the eye. The presence of this large fat mass 

 in the former location of the eye, the large reserve fat mass in the body, 

 the uniformly good condition of the fish and the low vitality, which 

 enables them to live for months without visible food, all argue against 

 the possibility that the struggle for food between parts was an active 

 agent in the degeneration of the eyes. 



* Gesammelte Abhandlungen, 1895. 



