323 THE EVOLUTION THEORY 



the light, and on the whole are not unlike eyes. That this sort of 

 structure should have arisen all at once through a ' mutation ' is in- 

 conceivable ; it can have originated only from simple beginnings by 

 a gradual increase of its structure along with continual strict selection 

 among the variations which cropped up. They all depend upon com- 

 plicated ' harmonious ' adaptation, and cannot possibly have been 

 derived from mutations, that is, from ready-made structural ' constel- 

 lations,' unless we are to call in the aid of the miraculous. But 

 lanterns of this kind are found in many different kinds of animals — in 

 Schizopod Crustaceans, in shrimps, in fishes of different genera and 

 families. Many fishes have long rows of luminous organs on the sides 

 and on the belly, and these probably serve to light up the sea-floor 

 and facilitate the finding of food ; in others the luminous organs are 

 placed upon the snout just above the wide voracious mouth, and in 

 that position they have undoubtedly the significance attributed to 

 them by Chun, namely, that they attract small animals, just as the 

 electric lamps allure all sorts of nocturnal animals, and especially 

 insects, in large numbers to their destruction. But not fishes only, 

 but molluscs, e. g. the Cephalopods of the great depths, have developed 

 luminous organs, and one species of Cephalopod has about twenty 

 large luminous organs, like gleaming jewels, ultramarine, ruby -red, 

 sky-blue and silvery, while in another the whole surface of the belly 

 is dotted over with little pearl-like luminous organs. Even if we 

 cannot be quite clear as to the special use of these lanterns of deep-sea 

 animals, there can be no doubt that they are adaptations to the dark- 

 ness of the great depths, and when we find the same adaptations (in 

 a physiological sense) in many animals belonging to the most diverse 

 groups, there is no possibility of referring them to sudden mutations 

 which have arisen all at once in these groups with no i-elation to 

 utility, and yet have not occurred in any animals living in the 

 light. Only ' variations ' progressing and combining in the direction of 

 utility can give us the key to an explanation of the origin of such 

 structures. 



The same is true of the eyes of deep-sea animals. It was believed 

 at one time that all the inhabitants of dark regions had lost their eyes. 

 This is the case with many cave animals and the inhabitants of the 

 lightless depths of our lakes, but in the abyssal zone of the sea it is 

 only some fishes and Crustaceans whose eyes have degenerated to the 

 vanishing point. Moreover, the disappearance apparently occurs in 

 species which are restricted to the ocean-floor in their search for food, 

 which therefore can make more use of their tactile organs than of 

 their eyes, for while the ocean-floor undoubtedly contains over wide 



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