288 



PBESH-WATEE AQUAEIA. 



parents, whicli are, as a rule, of a dark reddish colour, but 

 sometimes, owing to the locality in which they are found, 

 black. When one considers what excellent scavengers, how 

 prolific, and how suitable as food for fish, these Gammari are, 

 one wUl naturally come to the conclusion that they are quite 

 worthy of encouragement in those waters in which trout and 

 other fish are preserved. 



The Water-louse {Asellus aquaticus) (Fig 167) is a very 

 common crustacean. It is so like in appearance to the wood- 

 louse or " garden-pig," that no description is necessary. It 

 does not swim, but is found crawling abont the bottom or 

 weeds of ponds and ditches. A. aquaticus is a usefid scavenger 

 in the aquarium, for it lives principally upon decaying vege- 

 table matter. I have, how- 

 ever, more than once, seen 

 it apparently feeding upon 

 animal food. The female 

 Water-louse carries her 

 eggs in a membranous sac 

 attached to the under-part 

 of her body, and there the 

 young remain for some 

 time after they are hatched. 

 The period which elapses 

 between the laying of the eggs and the young AselU leaving 

 their mother's care is generally about six weeks. The young 

 are of a very light colour. The male is much larger than the 

 female, and is abont ^in. long. These creatures breed freely 

 in captivity, and thus provide fish and other inhabitants of 

 the aquarium with suitable food. They are easily obtained, 

 for they are nearly always found crawling about the mud or 

 weeds which are taken from either stagnant or slow-running 

 water. The vessels in which Aselli are kept mtist be securely 

 covered, or their inmates wiU be certain to escape, and, as 

 a consequence, die. 



The tiny crustaceans which are well called Entomostraca, 

 or " shelled insects," are all more or less covered with a shelly 

 envelope. They are both very interesting and very useful in 



Fig. 167. Water-loose 

 (asellus aquaticus). 



