102 THE STORY OF LIFE IN THE SEAS. 



the Pteropods. These creatures are provided 

 with a pair of muscular lobes of the body, which 

 have been compared to wings. By means of 

 these they are able to swim through the water. 

 Some of them are provided with delicate little 

 glassy shells, but in others the body is quite 

 naked. We may regard the Pteropods as 

 the most highly modified forms of Gastropods 

 adapted for a pelagic life. 



In both the Arctic and Antarctic seas this 

 group occurs in immense numbers, and it is 

 supposed to form not an inconsiderable pro- 

 portion of the food of the gigantic Eight- 

 whales. They also occur in the Temperate and 

 Tropical zones, and indeed there are actually 

 more genera and species there than in the colder 

 regions to the North and South. 



The Insect world is. represented at the surface 

 of the ocean by a curious little Bug called Halo- 

 bates. It is not uncommonly found in tropical 

 or subtropical seas feeding upon dead Salps or 

 Jelly-fish, and when disturbed scuds over the 

 surface after the manner of many of the Insects 

 living on our inland ponds and lakes. It has 

 been described as an "ivory-legged fellow, 

 covered with a bluish- white down." As it is 

 essentially an air-breather like all adult insects, 

 its usual habitat is * on ' the sea and not in it, so 

 that strictly speaking it is not a member of the 

 Plankton. There is no doubt that under cer- 

 tain circumstances it can and does dive into the 

 water, and on these occasions it carries with it 

 for respiratory purposes a layer of air attached 

 to the ' bluish- white down ' covering the body. 



