Chap. xxii.J PROTECTIVE COLOURING. 



493 



coloured pieces of Weed, which are also most thickly covered 

 with Membranipora. 



The small fish {Antemiarius) is in the same way coloured 

 Weed-colour with white spots. Even a Planarian worm, which 

 lives in the Weed, is similarly yellow-coloured, and also a 

 Mollusc {Scylhea pelagica). The white patches on some of 

 the Crabs, no doubt, represent also, to some extent, the white 

 shells of Barnacles, though these are not very abundant in the 

 Weed. A small Crab, Nautilograpsus minutus, which varies 

 very much in colour, is very abundant amongst the Weed, and 

 constantly to be found also in large numbers hanging on to 

 floating logs and similar objects elsewhere, and in these cases 

 the white patches on its body correspond closely with the 

 barnacles by which the logs are covered. These little crabs 

 vary extremely in the arrangement and forms of the white 

 patterns on their backs, and we once found a number of them 

 (I believe of the same species) which were clinging to the 

 floats of the blue-shelled Pelagic Mollusc lanthina, and these 

 were all coloured, for concealment, of a corresponding blue. 



Pelagic animals generally seem to be either colourless or 

 specially coloured, with a view to protection from enemies 

 both above and below the surface of the water. Probably the 

 blue colour of Ia?ithitia and Velella is protective as resembling 

 that of the ocean water. Velella has serious enemies in the 

 oceanic birds and in turtles. We caught a small turtle {Chelo?ie 

 imhricata) which had its stomach full of Velelhe. There are 

 numerous other Pelagic animals thus coloured blue for protec- 

 tion, such as the Mollusc GlaucHS, Porpita allied to Velella^ 

 and some Salpce in which the nucleus is blue. There are also 

 blue MeduscE. 



The dark red-brown colour of the nucleus of most Salpce is 

 probably an imitation of that of floating seaweed, and it occurs 

 in several other Pelagic animals, as, for example, Felagone- 

 7nertes. The extraordinary transparency of most Pelagic 

 animals, is, no doubt, a protective contrivance. In both 

 Salpa and Felagoiiei/iertes, above referred to, almost the entire 

 body, with the "exception of the smaller parts coloured brown, 

 as described, are colourless and transparent, like glass. It is 

 extremely difficult to see these transparent animals, when one 

 attempts to collect them from a boat. 



Almost all classes of land or shore animals seem to have 

 contributed to the Pelagic fauna forms which have become in 

 most cases extremely modified to suit their changed mode of 

 existence. Amongst Mammals there are the Whales and Por- 

 poises, the ancestors of which, no doubt, long after they had 

 deserted the land and had taken to a Pelagic existence, came 



