STOCKING WATEES WITH FOOD 



do harm than good, such a number of our water- 

 beetles being carnivorous. They will probably 

 not harm adult fish, but they will destroy ova and 

 fry. I have known a Dytiscus marginalis kill a 

 trout of nearly a quarter of a pound in weight. 



In order to make sure of not introducing car- 

 nivorous water-beetles into a water, I think it 

 best as a rule not to introduce beetles at all. 

 Corixce are, however, so like beetles, that many 

 people call them beetles, and therefore I will give 

 a few points which will make them easily dis- 

 tinguishable from each other. In beetles, the 

 wing-cases (elytra) meet exactly in the middle 

 line, in Corixce and other water-bugs, the an- 

 terior wings, which resemble the elytra of beetles, 

 overlap, which causes the line on the back to 

 curve away to one side at the lower end. In 

 beetles the wings which lie under the wing-cases 

 are folded up on themselves, and when spread out 

 are much larger than the wing-cases. The 

 wings are transparent and very delicate. In 

 Corixce the posterior wings, which lie under the 

 hard and horny anterior wings, are a little 

 shorter than the anterior wings ; they are not 

 folded up on themselves and are not so delicate 

 and transparent as the wings of the beetle. 



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