1894.] Subterranean Fauna of North America. 741 
disuse; 6, The new variety or species or genus, as the case 
might be, would become persistent, as long as the conditions 
of total or partial darkness continued. 
Now these factors, so simple, so easily appreciated, that as 
early as 1802, Lamarck could see their force, though he only 
cited the case of the mole, for he knew nothing of cave ani- 
mals—these factors would seem to be adequate for the pro- 
duction of these eyeless forms. These results of disuse seemed 
adequate to Darwin himself, the founder of the doctrine of 
natural selection; and yet the extreme Darwinians or Neo- 
darwinians of the present day push aside or are purblind to 
these fundamental factors of organic evolution, and insist that 
the vera causa of the evolution of these blind forms is either 
natural selection or panmixia, and they likewise deny that 
there is any ground for the operation of the principle of trans- 
mission of acquired characters. 
Weismann, who has rendered such eminent service to 
biology, in establishing the principle of heredity on a physical 
basis, as is well-known, pushes aside all these factors and ex- 
plains the blindness of cave animals by a negative cause, 
“ panmixia," i.e, the absence of natural selection. In his 
“ Essays on Heredity " (1889) he claims that the small eyes of 
moles and of other subterranean mammals can be explained 
by natural selection, and remarks: “I think it is difficult to 
reconcile the facts of the case with the ordinary theory that the 
eyes of these animals have simply degenerated through disuse " 
(p. 86). He assumes that the degeneration of the eye of 
Proteus “is merely due to the cessation of the conserving in- 
fluence of natural selection," and, he adds farther on, “this 
suspension of the preserving influence of natural selection may 
be termed Panmixia.” And he even goes so far as to express 
the opinion that “that the greater number of those variations 
which are usually attributed to the direct influence of external 
conditions of life, are to be attributed to panmixia.” He thus 
substitutes for the positive, tangible factors of change of en- 
vironment, disuse and isolation, the negative and hypothetical 
one which he calls “ panmixia.” 
