CONDITIONS OF LIFE 



233 



skin, and elaborate ridges of sensitive papillae are present to a 

 varying degree on the head and body. 



In the underground streams of Cuba, and perhaps also in 

 Jamaica, are found the well-known Cuban Blind-fishes {Lucifuga^ 

 Stygicola) or "Pez Ciego." The streams inhabited by these 

 fishes first run above ground, then enter the ground, and finally 

 emerge again near the coast. They are in no place far below 

 the surface, and here and there the roofs of the channels are 

 cracked and broken, forming the entrances to the so-called 

 caves. The two forms represent the only fresh-water members 

 of a large and varied family of fishes known as Brotulids 

 (Brotulidae) , the majority of which live at considerable depths 

 in the oceans. They grow to a length of about five inches, 

 and the coloration varies from dark blue to pinkish. They are 



Fig. 92. BLIND-FISHES. 



A. Cuban Blind-fish (Stygicola dentatus),x about i ; B. Californian Blind Goby 

 (Typhlogobius calif orniensis), X i. 



quite blind, the eyes, which are comparatively well formed in 

 the young, degenerating in the adult and becoming covered 

 with skin (Fig. 92A). The head, however, is provided with 

 numerous minute sensitive barbels. 



It seems clear that the adoption of cavernicolous habits 

 inevitably leads to the loss of the body pigments and to the 

 degeneration of the eyes; and further, if this mode of life is 

 extended over a considerable period, the reduction of the 

 visual sense is compensated for by the special development or 

 improvement of some other organ or organs of sense. The 

 ridges of papillae present on the head and body in the Cyprino- 

 donts are regularly arranged, and, as might be expected, are 

 only slightly developed (if at all) in those species which possess 

 eyes, and reach their maximum development in the totally 

 blind forms. Their function is almost certainly the same as 

 that of the lateral line {cf. p. 202), enabling the fish to perceive 



