MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 119 



where it finds food ; and a small specimen has been found by Mr. Putnam a little paler than usual, 

 i. e., as pale as the darker specimens of G. peUucidus, but the eyes were normal, though it is doubt- 

 ful if it lives long enough in the cave to breed there. 



The nearest out-of-door ally of C. 'peUucidus is Cambarus affinis. On the other hand, the 

 nearest lucicolous ally .of C. hamulatus is perhaps C. latimanus. 



It is instructive to find that, in regard to the development of the eyes, and the slenderness, 

 size, and color of the body, these two cave crayfish closely resemble each other, though obviously 

 originating, as Professor Faxon states, from species belonging to quite different sections of the 

 genus Cambarus, and to a different, more southern, river valley. These facts appear to prove 

 beyond question that the cave species of crayfish in the United States have descended from quite 

 different species of Cambarus, belonging to different zoogeographical areas.* Had the two species 

 of blind crayfish been produced instantaneously by special creation, as popularly supposed and 

 advocated in the past by some naturalists, why should the accessory genital organs (gouopoda) 

 differ so much that on this account they belong to different sections of the genus Cambarus? 



The cave Phalangidse, or harvest-men, whose habits and distribution in Europe as well as the 

 United States, both as regards lucicolous and cavernicolous forms, have been given in detail in a 

 previous chapter, illustrate clearly the theory that certain subterranean forms, living deep in the 

 soil, under stones in the cave regions of both hemispheres, especially in France and Austria, have 

 been carried into caves, have survived the loss of out-of-door conditions, becoming adapted to 

 the new and strange environment, losing their eyes totally or in part from disuse of those organs, 

 and have bred true to the new specific characters thus established, and are now as unchangeable 

 as the physical conditions in which they live. 



The cave spiders in all important respects exemplify the same rule. They belong to, or are 

 closely allied to, genera rich in species in the cavernous regions they inhabit, and which live in 

 dark places. Although scarcely necessary in its changed environment, where there are no hydro- 

 graphic changes, no winter and summer, and few enemies to contend with, the most aberrant 

 form, the completely eyeless Anthrobia of Mammoth Cave, still spins a silk cocoon around its 

 eggs ; while in Weyer's Cave Nesticus pallidas Emerton spins a cocoon for its eggs ; and either 

 this species or its fellow troglodyte, Linyphia incerta Emerton, or both species, spiu a weak, 

 irregular web, consisting of a few threads. Is not this a useless habit, a simple survival of an- 

 cestral traits ? 



It was noticed that the number of individuals of different species was greater in the smaller 

 shallower caves, such as the Weyer and Carter caverns ; each of these groups of caves has three 

 species, while in Mammoth Cave there is but one, and the individuals are less common. More- 

 over, all are darker than Anthrobia, all have eyes, and the number of eyes is variable. These 

 facts show that Anthrobia and the eyed forms have originated from species living in partial dark- 

 ness at or near the mouths of the caverns. In Mr. Einerton's description of Linyphia incerta it 

 will be seen how variable are the number of eyes. From this it may be inferred that the specific 

 character of this form, as regards the eyes at least, have not been firmly established, and hence it 

 has only recently become a true troglodyte. 



In the foregoing examples we have as yet not discovered in this country any connecting links 

 between the eyed and blind or eyeless species of cave animals. But in a series of specimens of a 

 cave Myriopod, Pseudotremia cavernarum, which is abundant in the Wyandotte and Carter caves, 

 we have what we regard as good, if not complete, evidence that this cave form has directly origi- 

 nated from a common and widely distributed out-of-door form. The cave Pseudotremia has black 

 eyes, composed of from 12 to 15 facets arranged in a triangular area; of one hundred and fifty 

 specimens examined none were found to be eyeless. In a large cave like Wyandotte there is 

 little variation in this .species as regards size, proportion, or color (being white with a slight flesh 



* Dr. Joseph states that the Carniolan Cambarus etygius is very nearly allied to the American C. peUucidus. As 

 only a single dry specimen from one cave aud remains of the forceps or hand of another specimen have heen found in 

 another cave, it seems premature to draw conclusions from such limited facts. The question naturally arises why the 

 genus Cambarus, not hitherto found in Europe, should alone he represented in caves. Its appearance in such a situa- 

 tion and ou a continent where there are no other species of Cambarus, the genus Astacus alone living in Europe, has 

 been thought to be a fact adverse to a derivation theory. 



