124 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The cave spiders appear to differ only in the lack of eyes from their congeners out of doors, 

 their legs being scarcely longer than in the eyed species. In what anatomical respects nature has 

 compensated Anthrobia for the loss of eyes is not very apparent. 



It is in the blind cave insects that the tactile sense is -evidently hypertrophied. In Ehaphi. 

 dophora the antennae, palpi, and legs are very long and slender, even compared with out-of-door 

 wingless Locustarians, which have remarkably long antennas and hind legs. 



Still more clearly are the effects of a life in total darkness, resulting in the atrophy of the eyes 

 and hypertrophy of the appendages accompanied by a slenderness of the trunk, seen in the species 

 of Anophthaltnus, as a glance at any of our native species, when compared with our native species 

 of Trechus, will at once show. The same applies, though in a less marked degree, to Adelops and 

 Bathyscia. 



We will now review the facts known bearing upon the physiology of the tactile organs, involv- 

 ing the effects of sudden light, noises, and contact with these stygian forms, and it will be seen 

 how remarkable has been the compensation for the loss of eye-sight. As the most detailed and 

 striking results, and showing how completely nature has compensated these apparently hapless 

 forms for their loss of eye-sight, and how remarkable is the degree of adaptation to so great a change 

 of environment, we will cite the observations of Piochard de la Brulerie.* This author maintains 

 that the sense of touch compensates for the loss of eyes. In all blind Coleoptera, he says, there 

 is a tendency in their appendages to elongate, except in Claviger, which, living in the society of 

 ants, are cared for and fed by them. The hairs on the antennas and feet of blind insects are longer 

 than in eyed insects. The long, stiff hairs of Anophthalmus are more developed than in any eyed 

 Carabid.t This elongation is in direct relation to the loss of eyes, compensating for the latter 

 defect, and they are rarely, if ever, present in epigean ground beetles. 



This author also claims that the habits of the species of Trechus and Catops, which have well- 

 developed eyes, are such as to indicate that Anophthalmus and Adelops have respectively been 

 derived from them. The former habitually live in the open air, always seek obscure passages, and 

 even like to penetrate into caverns, where they at times reproduce, and where their successive 

 generations thus confined have lost by disuse organs become useless, at the same time that they 

 acquire in those organs which survive the perfection rendered necessary by the disappearance 

 of the organs of vision. 



He then adds that the number of species of Anophthalmus and Adelops is greater than 

 that of Trechus and Catops, and that the species are at the same time more localized. These 

 facts are due to a double cause: "The differences in the conditions of life are more accentuated 

 for the population of different caverns than for that of different points of the surface of the soil, 

 and thej r are more absolutely isolated in these small hypogeau worlds." 



De la Brulerie then asks whether insects deprived of eyes are capable of being impressed by 

 light. He first draws attention to Dr. G. Pouchet's essay in the Kevue et Magasin de Zoologie 

 treating of the action of light on eyeless dipterous larvas, wherein he proves that they are affected 

 by the luminous rays, though their movements are very simple compared with the complicated 

 movements of Anophthalmus or Adelops in seeking their food or in escaping danger. 



Indeed, though deprived of eyes, these beings act exactly as if they saw clearly; as if they not only felt the 

 impressions of the luminous rays which struck them, but appreciated the form of objects, both of those at a distance 

 and of those that they touch. Nothing in their behavior suggests that they are blind. We see them walk, run, stop, 

 explore the ground, seek their food, run from the fingers of the insect hunter who tries to seize them absolutely with 

 the same facility as insects provided with eyes (p. 469). 



When in a cave, the light of a candle surprises a blind Anophthalmus or a Pristonychus which 

 has eyes. Both act in the same manner. 



Light on the subject of adaptation to cave life is thrown by the recent studies of Graber, and 

 especially those of Prof. Felix Plateau. The habits and environments of the family Polydes- 

 midas, which are all blind, and of Geophilus and other blind Chilopod Myriopods, show that the 

 loss of eyes does not signify so much as would be the case with the eyed forms, which need or are 

 capable of withstanding more light and less moisture. Graber, on depriving a cockroach (Blatta 



* Annales de la Socie'te' Entomologique de France, 1872. 



t These hairs are very well represented in some of the figures on Plates XVIII and XX. 



