324 EVOLUTION AND ANIMAL LIFE 



lower depth there is no difference between winter and summer, 

 and still lower none between day and night. The bassalian 

 fishes inhabit a region of great cold and inky darkness. Their 

 bodies are subjected to great pressure, and the conditions of 

 life are practically unvarying. There is, therefore, among them 

 no migration, no seasonal change, no spawning season fixed 

 by outside conditions, and no need of adaptation to varying 

 environment. As a result, all are uniform indigo-black or 

 purple in color, and all show more or less degeneration in those 

 characters associated with ordinary environment. Their bodies 

 are elongate, from the lack of specialization in the vertebrae. 

 The flesh, being held in place by the great pressure of the 

 water, is soft and fragile. The organs of touch are often highly 

 developed. The eye is either excessively large, as if to catch 

 the slightest ray of light, or else it is undeveloped, as if the 

 fish had abandoned the effort to see. In many cases luminous 

 spots or lanterns are developed by which the fish may see to 

 guide its way, and in some forms these shining appendages 

 are highly developed. In one form (dEthoprora) a luminous 

 body covers the end of the nose, like the headlight of an engine. 

 Many of these species have excessively large teeth, and some 

 have been known to swallow animals actually larger than 

 themselves. Those which have lanternlike spots have always 

 large eyes. 



The deep-sea fishes, however fantastic, have all near rela- 

 tives among the shore forms. Most of them are degenerate 

 representatives of well-known types for example, of eels, cod, 

 smelt, grenadiers, sculpin, and flounders. The deep-sea crus- 

 taceans and mollusks are similarly related to shore forms. 



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The third great subdivision of marine animals is the littoral 

 or shore group, those living in water of moderate depth, never 

 venturing far into the open sea either at the surface or in the 

 depths. This group shades into both the preceding. The 

 individuals of some of the species are excessively local, remain- 

 ing their life long in tide pools or coral reefs or piles of rock. 

 Others venture far from home, becoming more or less pelagic. 

 Still others ascend rivers either to spawn (anadromous, as the 

 salmon, shad, and striped bass), or for purposes of feeding, as 

 the robalo, corvina, and other shore fishes of the tropics. 

 Some live among rocks alone, some in seaweed, some on sandy 

 shores, some in the surf, and some only in sheltered lagoons. 



