1 88 RAMBLES AND REVERIES. 



move with slow and laborious efforts or else with 

 quick and jerky movements within the microscopic 

 field. 



There is an object which for a long time has 

 seemed to be inviting attention by frisking across 

 the field, and sometimes remaining for a moment 

 within vision: what can it be? If fleas lived in 

 water, one might jump to the hasty conclusion that 

 it really was a young flea. Its antics are certainly 

 quite as fantastic as those of the " lively flea." This, 

 no doubt, explains why it is called the water-flea. 

 We must not, however, be misled by names. These 

 tiny creatures are very different from the ordinary 

 flea, as may be seen by looking at both objects 

 under a low power through the microscope. The 

 flea is an insect proper, with rudimentary wings, and 

 breathes the air like other insects. But if you 

 closely observe this nimble dweller in the water, you 

 will see that it has delicate appendages to the head, 

 like branched antlers. Moreover, its body is soon 

 perceived to be encased in an almost transparent 

 shell, having two valves, and its feet are prolonged 

 into plates, very much like the gill-plates of fishes, 

 only, of course, very minute. 



Water-fleas belong to a group of animals called 

 Entomostracans, which form a sub-division of Crus- 

 taceans, so that they are really related to shrimps 

 and lobsters. They are very ancient animals, and 

 can be traced back at least to Carboniferous times, 

 and seem to have been as numerous in the standing 

 pools of those vast forests which produced our coal, 

 as they are now. The covering, or carapace, of these 



