MAEINE ARTHROPODS 299 



Allied to the bristle -tails, and usually grouped with them in the 

 same order, are the little Spring-tails, some species of which may 

 often be seen huddled together on the surface of the water of a 

 rock pool. They are so small that, unless closely examined, they 

 may be mistaken for particles of floating inorganic matter which 

 have been blown into a sheltered corner of the pool, and this idea 

 may be strengthened by the fact that these minute creatures are 

 driven by the wind into such sheltered spots. But when we 

 disturb them their true nature immediately becomes apparent, 

 for they may then be seen to move about on the surface of the 

 water, sometimes creeping on the surface film, and clambering on 

 the adjacent rock or weed, or leaping more or less vigorously, in 

 which latter case their bodies do not become wetted, the surface 

 film remaining unbroken by their exertions. And even when the 

 rising tide drives the spring-tails into crevices where they remain 

 submerged, perhaps for hours together, their bodies still remain 

 dry, the water being kept off by numerous short bristles and 

 prominences with which they are furnished. 



"When we examine a spring-tail by means of a lens we observe 

 that it has no traces of wings, but that each of the three seg- 

 ments representing the thorax bears a pair of short legs, and that 

 the abdomen consists of only five or six segments. The head is 

 furnished with a pair of jaws, and the antennae, which are short 

 and thick, are composed of but few joints never more than six in 

 number. 



Some spring-tails live among the refuse washed up on the 

 beach, where they may be seen jumping about in company with the 

 sandhoppers when the material is disturbed. Such is the case with 

 Isotoma maritima, the illustration of which shows the forked 

 tail that enables the little animal to jump about so vigorously. 

 But some of the marine spring-tails are not so true to their name, 

 since they are not provided with this characteristic jumping organ, 

 and have to content themselves by creeping about slowly with the 

 aid of their short legs. One of these springless spring-tails (Anurida 

 maritima) is one of the commonest of the group, and is distributed 

 over almost every part of our coast. 



Passing over several orders of insects which do not seem to have 

 any marine representatives, we come to the Diptera or two-winged 

 insects, of which the familiar house-fly is a type, and here we have 

 to deal with those troublesome creatures that literally swarm in 

 the neighbourhood of the matter washed up to the highest level 



