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Europe, nnder huge boulders, wheie liglit can never penetrate, are 

 found fauna specially adapted to such conditions of life ; blind 

 spiders, beetles, etc., occur in such positions. Many ento-parasites 

 are eyeless, and this fi-om their habitat we might expect to be 

 the case ; some have only rudimentary eyes. The number of 

 known species of blind cave insects amounts to hundreds. 

 Associated with these we find blind spiders, Crustacea, and 

 Myriapoda. The so-called blind crab of the Kentucky caves 

 is said to have rudimentary eyes; whilst other Crustacea (as Stygia, 

 Titanethes alhus, etc.), seem to be totally bhud. A list of these, 

 with illustrations, is given in the work of Putnam and Packard on 

 the Mammoth Cave of Kentucky. The " Challenger " expedition, 

 and the literature in relation thereto, will afford additional illus- 

 tration of the large number of blind invertebrates. Totally blind 

 crustaceans were found Uving at a depth of over 2000 fathoms. 



While darkness so complete as to prevent all use of the eye as an 

 organ of hght has led to the degradation of its structure, we should 

 be guilty of too hasty generalization, if we should hence formulate 

 a law that lack of light must necessarily lead to total or partial 

 blindness. Insects having weU-developed eyes are found inhabit- 

 ing the same spots as blind insects. Dr. Semper says that in some 

 caves in the Philippines and Pelew Islands, which he had personally 

 explored, he found in spots where absolute and total darkness 

 reigned, only insects tvith eyes. Again, it is known to most ento- 

 mologists that in all species of the cave beetle Machmrifes, the 

 females only are blind, while the males have well-developed eyes, 

 yet they live together in absolute darkness. I have not been able 

 to ascertain whether or not, at certain seasons, the female becomes 

 phosphorescent ; if this be so, it might help to account for the 

 sexual difference. These facts would appear to show that total 

 blindness in a particular species may arise from causes other than 

 absence of light alone. 



Enough, perhaps, has been said with reference to the special 

 organs of sight. "We have ah-eady intimated that in light we have 

 something more than a luminous energy. Sun-light has its heating 

 and its chemical powers, and these affect the animal as they do the 

 vegetable organism. Animals in general breathe with less intensity 

 in the dark than in the light ; at all times they are burning carbon, 

 but the activity of its consumption is greatest in the light. Light, 



