130 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



(3) The cases of loss of the power of sight are either to he regarded as arrests of development daring larval life, 

 or as the consequence of a gradual reduction (up to extinction) through disuse. 



While a great number of cases of the first category may be enumerated, the shrimp ( Troglo- 

 caris schmidtii), living in subterrauean waters, and the large Gambarus stygius afford striking 

 examples of the loss of the power of sight by retrograde development. Both of these large 

 species of Crustacea have eye-stalks (Augapfel) of the same shape as in their allies of the upper 

 world, but without a trace of the refractive medium or of nervous elements. They are therefore 

 completely blind. The appearance of a sense organ in the usual external form without the 

 internal contents, without endowment with the faculty of exercising the sense, would be absurd 

 if we did not take into account the fact that the ancestors of these animals were provided with 

 normally constructed eyes. This view is confirmed by Dr. Joseph's discovery that the embryo of 

 Troglocaris schmidtii is provided in the egg with eyes* The present developmental history of each 

 individual of this remarkable animal repeats briefly, and with evident truth, the history of the 

 species in the distant past. 



Of another Crustacean, also blind — i.e., Niphargus stygius — Joseph found in the pools of water 

 in the outer partially dark rooms of several caves some individuals with distinct corneous facets, 

 crystalline lenses, optical rods, and nervous elements, but existing in small numbers and provided 

 with a slightly developed pigment layer, while in other individuals the eyes seemed reduced to the 

 condition of simple ocelli, like those of spiders. From all the cases which loss of the power 

 of sight proves, there are those of the oldest date which show them losing, besides the former, 

 every trace of eyes, also every indication of the same in embryonic life; and, on the other hand, 

 specimens occur which, although in want of a definite power of sight, still in embryo possess the 

 germs of organs of sight, and possess in a definite condition the external shape of such organs. 



(4) As the last effort to compensate for the loss of sight there is the unusual development of 

 tactile organs. In a species of Coleoptera, Anophthalmus capillatus, also in an Arachnid (Siro 

 cyphopselaphus) allied to Cyphophthalmus duricorius, both of which occur in a Croatian cave, there 

 is, in the place on the head where usually in the out-of-door genus Trechus and in Cyphophthalmus 

 duricorius the eyes are placed, a slender small tubercle provided with a fine tactile hair. To the 

 peculiarly formed interior of the tubercle there passes a fine nerve sent off from the suboeso- 

 phageal ganglion. In place of this tactile hair the species of other blind beetles ( Amaurops) pos- 

 sess a thick tactile bristle, or a delicate tactile rod, which rises from a tubercle with a rough nod- 

 ular surface. A species of the Podurid genus Anurophorus, discovered by Dr. Joseph, also pos- 

 sesses in place of eyes tactile hairs. 



For the tactile hairs of our American species of Anophthalmus and their position, the reader is 

 referred to the figures on Plates XVIII and XX. Those of Anophthalmus tellkampfii were omitted 

 by the artist. De la Brulerie, as stated on p. 124, has drawn attention to the fact that such tactile 

 hairs are not well developed in epigean Carabidse. In the figures of Anophthalmus eremita and 

 A. pusio the two tactile setae on the head are not represented ; whether they are present I can 

 not at the present writing of this paragraph state, as my specimens are not accessible. 



By reference to PI. XIX, figs. La, 3a', 3a", and 3a'", it will be seen how well developed are 

 the olfactory setae on the antennal joints. Whether such highly modified setae are to be found 

 on the antennae of epigean Caribidae is an interesting question. The olfactory organs, as we sup- 

 pose they are, of Adelops, are represented by Fig. 4. The palpi of none of these cave beetles are 

 supplied with organs of special sense. 



APPARENT EXCEPTIONS AND OBJECTIONS TO THE OPINION THAT A LIFE IN TOTAL DARKNESS 

 NECESSARILY INDUCES ATROPHY OF THE EYE OR BLINDNESS. 



A number of objectors and critics have strenuously opposed the view that absence of light 

 causes blindness or atrophy, partial or total, of the organs of vision. We do not refer to the gen- 

 eral belief advocated by naturalists and others of a former generation that blind cave animals 

 were specially and suddenly created isolated types of life existing in harmony with their sur- 

 roundings. 



* The microscopical and alcoholic specimens here referred to were demonstrated in the session of the Silesian 

 Society for the National Culture in Breslau for Novemher 10, 1875. 



