176 THE DISTRIBUTION OF 



translucent bodies it would seem as though they could 

 be very readily adapted to the pelagic life. As two 

 interesting forms mention may be made of the trans- 

 parent larva of the eel, called Leptocephalus, because 

 its relation to the parent was for long unknown, and the 

 glass crab (PhyUosoma), which is the larva of the rock 

 lobster, but was similarly for long regarded as an 

 independent organism. 



Very remarkable is the presence in the open sea of 

 the members of an insect genus, Halobates, a kind of 

 bug, related to the forms which skim over the surface 

 of fresh-water ponds. Some fifteen species of Halobates 

 are known from the warmer parts of the oceans. The 

 insects appear to be perfectly pelagic in that even the 

 eggs are produced in the open, but they may also 

 approach shores, for what reason is not known. The 

 female carries the eggs for a time attached to her own 

 body, and the young have been found on floating solid 

 bodies in the sea. Wings are completely absent, and 

 the body is covered with a greyish pubescence, which 

 shines in the sunhght. The animals breathe air, and 

 belong rather to the surface of the ocean than to its 

 waters. 



In contrast with these plankton or drifting forms, 

 we have in the open sea a number of powerful swimmers 

 (nekton) able to make headway against the currents. 

 The most important of these are the whales and their 

 aUies, whose distribution is tied to that of the animals 

 upon which they prey. Thus the huge cachalot or sperm 

 whale {Physeter macrocephalus) is foimd especially in 

 warm seas, where it finds the large cuttles upon which it 

 feeds. The related bottle-nose (Hyperoodon), which also 

 lives on cuttles, occurs iu colder seas, and is found 

 especially in the North Atlantic. The whalebone whales 



