138 MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 



to cave animals : "As it is difficult to imagine that eyes, though useless, could be in any way 

 injurious to animals living in darkness, I attribute their loss wholly to disuse" (p. 142). On the 

 next page he writes: "By the time that an animal had reached, after numberless generations, the 

 deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and 

 natural selection will often have effected other changes, such as an increase in the length of the 

 antennae or palpi, as a compensation for blindness." 



It may be that the struggle for existence goes on even in the darkness of caves, and that the 

 "fittest" of the limited population survive by reason of their adaptation to their untoward sur- 

 roundings. How adverse to life of any sort caves are may be realized when we consider that only 

 the lowest plants, and only a very few of those, live in caves. Without doubt the germs of fungi 

 and the seeds of the higher plants are carried into the caves by freshets in subterranean streams 

 and through sink-holes. Why, in spite of the darkness, we should not find more fungi even, and 

 why one or two of the green algae should not flourish in the pools and brooks of caves, or why the 

 seeds of the higher plants should not germinate, even if the plants do not bear fruit, can only be 

 explained by the absence of light; and perhaps this is an important cause of the absence of all 

 plant life in the ocean below a depth of about 300 to 500 fathoms. Certainly there are ample 

 means for the colonization of caves by vegetables ; the temperature, moisture, and inorganic food 

 are more favorable than the sum total of conditions on alpine summits or in the high polar regions, 

 or in hot springs. 



Animal life can apparently withstand greater physical obstacles than vegetable. As regards 

 the struggle for existence, it possibly exists to a limited extent in cave animals. There is 

 probably not enough vegetable or decayed animal food for all the animals, and some may die of 

 hunger. The carnivorous beetles and Arachuida perhaps have a less favorable chance to obtain 

 living food than the Crustacea, for the blind crayfish have a tolerable abundance of food in the 

 Osecidotsea, perhaps the most abundant form found in caves containing underground waters. 



We may, with Darwin, for convenience, use the phrase " natural selection " to express the 

 process by which the cave fauna was produced, but such a term to our mind expresses rather 

 the result of a series of causes than a vera causa in itself. There is of course no doubt but that 

 many animals carried by different means into caves cannot thrive there, and consequently die. It 

 is only those which have been able, by certain peculiarities of their life in the upper world allied 

 to cave existence, to adapt themselves to cave conditions, which permanently breed there. Such 

 forms, it is convenient to say, have been by nature selected and are successful in colonizing the darkest 

 and most forbidding and apparently hopeless corners in the earth's crust. But such a phrase as 

 " natural selection," we repeat, does not to our mind definitely bring before us the actual working 

 causes of the evolution of these cave organisms, and no one cause can apparently account for such 

 a result. There is rather a complex assemblage of physical causes, all working together, to secure 

 a harmonious result. The most important and potent of these causes, when we study them under 

 such appreciable, because so extraordinary,, conditions as the physical features of cave existence, 

 would seem to be the following: 



1. Change in environment from light, even partial, to twilight or total darkness, and involving 

 diminution of food, and compensation for the loss of certain organs by the hypertrophy of others. 



2. Disuse of certain organs. 



3. Adaptation, enabling the more plastic forms to survive and perpetuate their stock. 



4. Isolation, preventing intercrossing with out-of-door forms, thus insuring the permanency of 

 the new varieties, species, or genera. 



5. Heredity, operating to secure for the future the permanence of the newly originated forms 

 as long as the physical conditions remain the same. 



Natural selection, perhaps, expresses the total result of the working of these five factors, 

 rather than being an efficient cause in itself; or at least constitutes the last term in a series of 

 causes. Hence Lamarckianism in a modern form ; or, as we have termed it, Neolamarckianism, 

 seems to us to be nearer the truth than Darwinism proper or " natural selection." 



The factors of organic evolution such as we have mentioned are of course theoretical, and the 

 critic or unbeliever in a theory of descent demands facts in demonstration of the truth of the 



