216 Flow 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 Wewropfera, and on the whole are a bad lot on a fish farm. 
Most of the larve 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 
important 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. Limneus pereger. Fig. 33. Z. aurtculartus. 
snail is Limmneus 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 auriculartus ) 
is an excellent one. It grows larger than Z. ferveger, and is 
prolific. 
The trumpet snail (ZL. stagnalis) is a very handsome and 
useful molluse in large waters or ponds, but does not thrive in 
