MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
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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. pellucidus, but the eyes were normal, though it is doubt¬ 
ful if it lives long enough m the cave to breed there. 
The nearest out-of-door ally of G. pellucidus is Gambarus affinis. On the other hand, the 
nearest lucicolous ally of G. hamulatus is perhaps G. 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 (gonopoda) 
differ so much that on this account they belong to different sections of the genus Cambarus 1 ? 
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 pallidus Emerton spins a cocoon for its eggs; and either 
this species or its fellow troglodyte, Linyphia incerta Emerton, or both species, spin a weak, 
irregular web, consisting of a few threads. Is not this a useless habit, a simple survival of an¬ 
cestral traits 1 
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. Emerton’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 cavernanm, 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 W T yandotte 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 stygius is very neaTly allied to the American C. pellucidus. As 
only a single dry specimen from one cave and remains of the forceps or hand of another specimen have been 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 be represented in caves. Its appearance in such a situa¬ 
tion and on 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. 
