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 (Phyllosoma), 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 sunlight. 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 
allies, whose distribution is tied to that of the animals 
upon which they prey. Thus the huge cachalot or sperm 
whale (Physeter macrocephalus) is found 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 in colder seas, and is found 
especially in the North Atlantic. The whalebone whales 
