CRUSTACEA. 



449 



called the Spongilla fluviatilis (fig. 994). It is composed of siliceous 

 spiculae, in which the animal dwells, and when dry it very much 

 resembles the sponge we commonly use. It soon dies when removed 

 from the water. 



FIG. 994. Fresh-water Sponge, 

 magnified (showing spicuies). 



FIG. 995. Fresh-water Shrimp. 



CRUSTACEA. 



FIG. 996. Woodlouse. 



The Upper Wandle does not contain the Crayfish (A stacus fluviatilis}, 

 which I have often caught in the New River, Lea River, and Thames, 

 m the latter of which they abound at and above Oxford. I have 

 placed many in our river, but they have disappeared, which is another 

 failure in acclimatization. From this creature the Bisque soup of the 

 French is made. 



One aquatic species of Crustacean is of great value to us, the 

 Fresh-water Shrimp (Gammarus fallax, fig. 995). It exists literally by 

 myriads at the bottom of the river under every stone, and affords 

 abundance of food for the trout, which are very fond of them. 



Another Crustacean is terrestrial, and does us much mischief. It 

 is the Woodlouse (Oniscus asellus, fig. 996), of which there arc 

 more than one species. It delights to sally forth by night to devour 

 the delicate parts of the plants in our glass-houses, and it is especially 

 annoying to notice the injury they do to the roots and young shoots of 

 our valuable orchids. The gardener traps them by cutting a potato 

 in half, scooping out a portion, and turning the cavity downwards, when 

 the creatures collect underneath, and can be taken and destroyed. 



Perhaps, however, the best remedy for woodlice is the toad, which 

 eagerly devours them, and no good gardener is ever without his pet 

 toads, who thus do him much service. 



To return to the water : there are many microscopic species of 

 crustaceans, such as the Cyclops, which are supposed to afford food for 



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