MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 131 



In his excellent chapter on the influence of light* Semper, after remarking that " total dark- 

 ness gradually destroys the eyes of animals originally possessing them, for, since these organs 

 are absolutely useless in such circumstances, in the course of generations they must gradually dis- 

 appear, according to the law of degeneration, in consequence of their disuse," a few pages beyond, 

 however, adds: 



But, though we are thus fully justified in saying that darkness so complete as not to allow of the eyes being 

 used at all has in most cases exercised an injurious effect on their existence and structure, it would nevertheless he 

 wholly false to assume that the lack of light must necessarily lead to total or partial blindness. We know of a number 

 of facts directly opposed to such a conclusion. Among the numerous cave insects there are many which have well- 

 developed eyes and yet inhabit the same spot as blind species. In some caves in the Philippines andthe Pelew Islands 

 which I myself explored I found in spots where the most absolute and total darkness reigned only insects with eyes. 

 Hadencecus, a species of grasshopper which lives in the caves of Kentucky, has well-developed eyes like other ani- 

 mals found there at the same time. Why should not darkness have had the same effect on these animals as on others 

 which have in fact become blind? It might be said — in fact it has been said — that the cave animals which can see 

 have migrated into the cave only within a short period, and have not been exposed to the influence of the darkness 

 long enough to suffer ; while the blind or half-blind, having entered the caves at a remote period, have lost the use 

 of their eyes, wholly or partially, in consequence of long desuetude. But this explanation contradicts the fact, pre- 

 viously mentioned, that every mole, Pinnotheres, etc., originally had eyes apparently capable of further development 

 and of perfectly fulfilling their normal function; and that the influence of darkness is proved to be direct in each 

 individual, and not hereditary. This explanation is also quite decisively contradicted by a fact which is little 

 known generally, and even among zoologists is familiar to none but entomologists. I owe my own knowledge of it 

 to my friend Dr. Hageu, of Cambridge, United States. In all the species of the cave beetle Machayrites the females 

 only are blind, while the males have well-developed eyes. In spite of this they both live together in ab olute dark- 

 ness. This proves that the same result— total blindness — may come from different causes ; for we may fairly regard 

 it as impossible that in the last-named case the darkness of the cave has affected tho females alone and been inef- 

 fective on the males ; hence the blindness of the former cannot be caused by the darkness. In confirmation of this 

 statement I may also adduce the fact that there are many blind or half-blind animals which live in well-illuminated 

 situations, where the moderate intensity of the light would allow them the full use of the eyes. This is the case, for 

 instance, with many bivalves — all fresh-water bivalves and many sea bivalves — with various Annelida (Chaetogaster), 

 Crustacea (Cyclqpidffl), and others. I myself have found a perfectly blind small species of Cymothoe living in slightly 

 brackish water in a basin overshadowed by limestone rock, but in spots where full daylight could penetrate. 



In the case of Hadencecus it should be remarked that, so far as we have observed in Mammoth 

 and the other caves we have examined, this cricket not only lives in the entirely dark regions of 

 the caves, but abounds in twilight and near the openings ; i. e., in places where the species of 

 Anophthalmus and Adelops, etc., are never found. It is a twilight species, and, being active 

 in its habits, may migrate from one part of the cave to another. Moreover it occurs, as will be 

 seen on page 69, in many small partially lighted caverns and grottoes. There is no reason why 

 those individuals which occur in total darkness may not cross with those living near the entrance, 

 and thus the eyes may remain unimpaired. Moreover the eggs of this species have not yet been 

 discovered, and we do not know whether it oviposits freely in totally dark or iu partially lighted 

 localities in the cave. 



In the case of the Machaarites (which does not occur in American caves), it may be said that 

 further investigation may show that the species which have eyeless females and eyed males may 

 be twilight forms rather than denizens of "absolute darkness." Machserites is stated b} r Bedel 

 to constitute a subgenus of Bythinus, "a numerous genus, spread over all of Europe and in the 

 United States. Most of the species are eyed and live in cool places under moss; some Southern 

 species are lapidicolous or cavernicolous. The reduction, more or less complete, of the visual 

 organs in the latter, and principally in the females, has served as the base of the subgenera 

 Machserites and Linderia, which comprise all the species found in grottoes." Of Machcerites spelceus 

 Miller only the female is known. Of the three other species no biological information is given by 

 Bedel. Of the three species of Linderia, L. armatus is represented by a male and L. clarce by a 

 female ouly. Machcerites cristatus, found at Ariege under an enormous stone before the entrance 

 of a cave, is represented by a single male, whose eyes were obliterated, while M. bonvouloiri, found 

 in moss, is represented by a male and female, both of which are eyeless. t 



* Semper's Animal Life as Affected by the Natural Conditions of Existence, 1831. 



i De Saulcy (Ann. Soc. Ent. Fr., 4 e ser. tome iii, p. 649), referring to a statement of Grenier's, that the develop- 

 ment or non-development of the eyes in Machcerites {Linderia) marim, as found in the cave of Villefranche, depends 



