216 



How to obtain it. 



ingly prolific, and there should be no real difficulty in introducing 

 them. 



One other class of insects claim our attention, namely, the 

 dragon flies, of which there are some fifty varieties. They belong ' 

 to the Neuroptera, and on the whole are a bad lot on a fish farm. ! 

 Most of the larvae are very predacious, and the curious mask with 

 which they are provided has in close connection a pair of powerful 

 pincers, which they shoot out to catch their prey. They have 

 also equally powerful jaws, with which to dispose of any insects 

 or little fish they may catch. This sort of thing may be interesting, 

 to some observers, to watch in an aquarium, but anything but 

 profitable in trout fry nurseries. 



We now come to a class of creatures that play a most 

 mportant part in the economy of fish ponds, and these are the 

 Mollusca, including the Gasteropoda, or snails, and the Conchifera, 

 or bivalves. As in other classes in this also, the common varieties 

 are the most important to fish culturists. The commonest water 



Fig. 32 Limncpits fere^er. 



Fig. 33. L. anricularins. 



snail is Limnceus pereger, and if it should not be naturally present 

 in any water under cultivation, it should be introduced by all 

 means. Even in waters where it occurs naturally, but not 

 plentifully, it is a great help to introduce a few to augment the 

 stock ; it is an ascertained fact that with snails, as with larger 

 stock, the breed occasionally seems to get " stale," and almost 

 dies out, and the introduction of a number from elsewhere is a 

 distinct advantage. 



For very deep still waters the ear snail {Limnaus auricularis) 

 is an excellent one. It grows larger than Z. pereger, and is 

 prolific. 



The trumpet snail (Z. Stagnalis) is a very handsome and 

 useful mollusc in large waters or ponds, but does not thrive in 



