234 PROCEEDINGS OF THE NATIONAL MUSEUM. vol xxv. 



divide and reached the source of some other streams. As in Viroinia, 

 West Virginia, Kentucky, Tennessee, and Indiana many of the small 

 streams have their sources in cave streams it is easy to understand that 

 C hartoni is of common occurrence in the caverns of the region. I 

 have observed and collected the species in several caves in Indiana and 

 Kentucky in company with C. pellucidus and have found it abundant 

 in several caves in Virginia and West Virginia where C. 2>dh(cidu>< is 

 unknown. In one of the latter caves I collected an albinistic specimen 

 which is quite indistinguishable from others from the same locality 

 now that the alcohol has bleached them, and I have seen similar speci- 

 mens in localities where there were no caves. 



A review of the characters peculiar to C. hartoni tenebrosns, for by 

 that name the cave-dwelling form may be distinguished, shows that 

 there is a tendency in them to approach the characteristics of 0. pellu- 

 cidus. At tirst thought it seems as if this might be due to interbreed- 

 ing, but there are some difficulties in the way of such an explanation. 

 In the tirst place the species exist in the Mammoth Cave in nearly 

 equal numl)er, and the females of both have been collected while in the 

 egg-bearing state. The ova of C. hartoni are large, those of C. 2)eUii- 

 cidus are small, and no \ ariation in the size of the eggs such as would 

 probably result from crossing has been observed. The females of C. 

 hartoni., and the males as well, will average much larger than C. jpellu- 

 cidus and are reported by the guides to kill and eat the blind species, 

 a habit that, to say the least, would hardly be conducive to extensive 

 crossing of the two species. CkiynharuH hartoni and C. ^^Mveidus are 

 perfectly distinct species and could, without much straining of facts, 

 be regarded as generically distinct. The greatest diti'erences are found 

 in the structure of the sexual organs, and in a group which exhilnts 

 such marked specific variation in these organs it seems extremely 

 proba})lc that there is a reason for such differences, and that between 

 species so unlike interbreeding would be extremely difficult if not 

 impossi))le. There are known in the United States three other species 

 of blind cave-inha])iting crayfishes and, while they undoubtedly have 

 acquired their characters independently, they all resemble C. ]}elhicidus 

 (juite closely. Slenderness of body and appendages, and length of 

 antennii? are as characteristic of them as is the loss of eyes and color. 

 They are conditions brought about by their environment. C. lyellu- 

 cidus alone is characterized by excessive spininess, which evidently is 

 either a condition inherited from its ancestors or one which has been 

 developed in response to the peculiar conditions obtaining within its 

 habitat. It will be seen, therefore, that C. hartoni tenehroHUH resembles 

 all the blind species in the reduction in size of the eyes, and the increase 

 in size of the antennas and the form of the body, moreover there is 

 indication (as shown by its spininess) of its having responded to the 

 peculiar conditions of Mammoth Cave just as C. pellucid as has. 



