LIFE ON THE OCEAN SURFACE. 569 



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

 birds and in turtles. We caught a small turtle (Chelone 

 imbricata) which had its stomach full of Velellas. There 

 are numerous other Pelagic animals thus coloured blue for 

 protection, such as the Mollusc Glaums, Porpita allied to 

 Velella, and some Salpce in which the nucleus is blue. There 

 are also blue Medusa?. 



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, Pelagonemertes. 

 The extraordinary transparency of most Pelagic animals is, no 

 doubt, a protective contrivance. In both Salpa and Pelagone- 

 mertes, 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 

 on shore regularly, like the Seal, at certain seasons to breed, but 

 at length acquired the power of even rearing their young in the 

 open sea. 



Amongst birds the Petrels are Pelagic in habit, the largest 

 amongst them being the Albatross. Of the various kinds of 

 Petrels we necessarily saw a great deal. They were our con- 

 stant companions in the Southern Ocean, following the ship day 

 after day, dropping behind at night to roost on the water and 

 tracing the ship up again in the early morning by the trail of 

 debris left in its wake. 



The Oceanic Petrels have reduced the science of flight to 

 the condition of a fine art. The flight of the Albatross has 

 always excited wonder and admiration, nevertheless, some of the 

 smaller Petrels fly quite as well. There are almost all gradations 

 to be observed in the powers of flight of different birds, in the 



