﻿CAUSES OF DEGENERATION. 



237 



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 agamst 

 an orc^an which is now not only useless, but deleterious." This process will con- 

 tinue until the organ has reached " so minute a size that its presence is no longer 

 a source of detriment to the organism, the cessation of selection will carry the reduc- 

 tion a small degree further; and then the organ will remain as a 'rudiment.'" 

 Since however, we can not consider that the force of heredity is everlasting, it will 

 eventually fail and the organ dwindle still further and disappear. This failure 

 of heredity, Morgan (" Animal Life," page 793) is unable to distinguish from the 

 effect of disuse without which " the reduction of organs is difficult to explain. 



The principles involved in this explanation are panmixia natural selection, and, 

 according to Morgan, disuse transmission. 



Weismann ("Nature," 1886, and " Essays," vol. 11, i) contended that cessation 

 alone or panmixia as he terms it, is sufficient to account for all degeneration. He 

 later gave up this view for his theory of germinal selection, of which more later. 

 Roux, starting with the then generally accepted view that acquired characters 

 are transmitted, 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. He emphasizes the fact that a reduced functional activity 

 continued for a long period reduces the functional possibility of an organ (page 

 176). The diminished use not only brings about this simple atrophy, but also 

 the reduction, bv stronger neighbors, to such a volume as is still of advantage to the 

 animal. Disused organs that are not in the struggle for room may maintain them- 

 selves a long time. The struggle among parts for food, which implies the principle 

 of compensation of growth of Goethe, need not take place through the withdrawal 

 of blood, but may take place through the more active osmotic selection by the 

 stronger 'organ of food that would otherwise go to the weaker. 



Without doubting that both these principles are active agents in degeneration, it 

 may be seriously doubted whether they were 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 eve, the large reserve fat-mass in the body, the uni- 

 formly 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. 



Kohl considers that "Der Grund, und direkter oder indirekter Anlass zum 

 Eintreten der Entwickelungshemmung ist Lichtmangel." The method of the direct 

 operation of the lack of light he conceived to be as follows : The ancestry of blind 

 animals lived where the light was uninterrupted and they had developed eyes. 

 They f'ot into an environment where the light was shut off more or less. The first 

 genera'tions retained their fully developed eyes without, however, being able to 

 put them to full use. In consequence during phylogeny other organs became 

 highly developed to compensate for the disuse of the eye. (Through natural selec- 

 tion >) Thus touch organs (Myxine, Siphonops) or the auditory organs {Talpa 

 and possibly Typhlichthys) became more highly developed. The eye was unneces- 

 sarUy higlily developed. A process of degeneration (Ruckbildung) began, which 



