GENERAL BIOLOGY 671 



V. and VL). The small fishes [Aiitennariiis marmoTatus, 

 MonacantJnis, Seinola, Syngnatkzcs pelagicus), the crabs {Planes 

 minutiLs), the prawns {Latreutes ensifei^us and Palcemon nalator), 

 and also the naked snails, in fact all the animals of the Sargasso 

 Sea, seem in regard to colours, shape (see for instance the 

 remarkable prehensile organs of the pectoral fins oi Antennarms), 

 and size, to be intimately adapted to life among the drifting 

 tufts of the Sargasso weed. The idea of the utility of these 

 adaptations is here unavoidable. The occurrence of blue fins 

 appeals to me as most striking, and this feature is specially 

 noticeable in Hippocampus (the sea-horse). The specimen 

 captured by us (see Fig. 71, p. 89) was reddish-brown, only 

 the fins, which have to be freely moved in the blue water, 

 being deep blue. Plate VL shows five different specimens of 

 the crab Planes ininiUuSy exhibiting all the varieties of colour- 

 ing presented by the Sargasso weed. This species ought to 

 be a splendid object for experiments in order to test the 

 possible effects of variation in the colour of the surroundings ; 

 AntennaiHus might possibly also be employed for this purpose, 

 but on an expedition like ours the idea of performing such 

 experiments had to be abandoned. 



What I have said here refers mainly to the Sargasso Sea, 

 which was examined by us in regard to the light-conditions at 

 different depths, as well as the vertical distribution and the 

 colouring of the animals. As to the animals of the coastal 

 waters and those of the bottom of the ocean I have much less 

 to say. In coastal waters the light-conditions are undoubtedly 

 very different from those in the open ocean. The large amounts 

 of suspended substances reduce the transparency of the water 

 and prevent the light rays penetrating so far as they do in the 

 clear tropical or subtropical ocean. Hermann Pol's interesting 

 experiments at Nice have already been referred to (see p. 252) ; 

 he went down in a diving dress as far as 30 metres, at which 

 depth red animals appeared black. 



Are the red, yellow, and blue colours of the coast-fish 

 (as shown on Plate VII.) to be explained as protective colours.'* 

 Are they adaptations to the red of certain algse and other 

 colours of the sea-bottom, like the gaudy paintings of the 

 coral-reef fishes ? Or are they to be considered like those 

 adaptations which Darwin has ascribed to sexual selection ? 



Still more difficult is it to frame any idea as to the laws of 

 colour in the abyssal region. Plate VIII. shows two bottom 

 fishes from deep water, just on the limit where the traces of 



