MAEINE ARTHROPODS 297 



sense of the word ; and of these the species that have been observed 

 are mostly inhabitants of warmer seas. 



It is noteworthy that all the insects which exhibit marine ten- 

 dencies are small, and they seldom, if ever, live permanently below 

 the surface. But few of them can swim. A few run on the surface 

 of the water, supporting themselves on the surface film after the 

 manner of water-gnats, whirligig beetles, &c., without ever being 

 wetted ; and these are said to feed on different kinds of floating 

 matter, and occasionally to dive below the surface. 



A rambler on the sea shore in the summer time will always meet 

 with plenty of insect life, but the number of species observed may 

 not be large : and omitting all those which show no decided pre- 

 ference for the coast, but are found in inland districts as well, we 

 find that by far the larger proportion live at or near the high-water 

 mark, where they feed on the refuse washed up by the waves. 

 Some species, however, live among the stones, or burrow into the 

 sand, between the tide-marks ; and these, as a rule, are not driven 

 inland by each advancing tide, but allow the sea to wash over them, 

 having at first protected themselves from disturbance by burrowing 

 or seeking other suitable shelter. 



These latter, like many of the insects that inhabit fresh water, 

 are well adapted to withstand prolonged immersion. Their bodies 

 are not capable of being wetted, a covering of short hairs effectu- 

 ally preventing the water from coming into actual contact with the 

 body. The openings of the breathing tubes (spiracles) are also 

 guarded by closely set hairs which prevent the water from entering ; 

 and, in some cases, the creatures are provided with special air-sacs 

 in which a supply of air is stored for use while the insect is shut off 

 from the external atmosphere. 



The lowest order of insects includes the so-called Bugs 

 (Rhynchota), which are parasitic on plants or animals. Quite a 

 number of these are to be found inhabiting fresh water, but only 

 one is truly marine hi its tendencies. This one is a small insect, 

 only about an eighth of an inch in length, and named &pophilus 

 (fig. 222). It has never been seen except between the tide-marks, 

 and occurs so near low- water level that it is submerged during the 

 greater part of its existence. But little is known of this peculiar 

 creature. Even its food has not been ascertained. As with the 

 other Rhynchota, but little change of form takes place during 

 growth, the young being very much like the adult in appearance. 



