Page:Popular Science Monthly Volume 57.djvu/409

Rh 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 'congenitally blind.' "So all the while the process of adaptation was going on, the antennæ 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 transmission, to have given rise to generations of blind animals. The continued 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 (b) 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.