110 INSECTS AT HOME. 



case with the silkworm, but at the end of the tail. With these 

 instruments she forms a cocoon shaped almost exactly like a 

 turnip, being round, and having a pointed projection from one 

 side. Within this cocoon, which soon becomes hard and water- 

 tight, and is fastened to the stem of a water-plant, the eggs are 

 placed ; and in a time varying from a fortnight to six weeks, 

 according to the warmth of the weather, the larvse are hatched. 

 About fifty or sixty eggs are placed in one cocoon, and by this 

 extraordinary provision they are preserved from harm until the 

 larvEe are able to escape into the water and shift for themselves. 

 They are very small at first, but rapidly increase in size until 

 they attain the length of three inches. 



One of these larvse is shown at Fig. /, and is represented as 

 partly grown. It is soft, fat, and dusky in colour, and feeds 

 voraciously on molluscs and other aquatic animals, as might be 

 inferred from the large and curved jaws. It is one of the air- 

 breathing larvse, and is therefore obliged to come frequently to 

 the surface in order to take in a supply of air, which is done by 

 means of a filamentous appendage at the end of the tail. 

 Somewhere about July the larva has completed feeding ; and 

 then leaves the water and crawls up the bank, searching for a 

 soft spot in which to burrow. Here it sinks its tunnel, and 

 forms an oval cocoon, in which it awaits its change into the 

 pupal state. 



The Beetles belonging to this group, being, like the larvse, 

 air-breathers, are forced to come to the surface for the purpose 

 of respiration ; and they contrive to carry down a supply of 

 atmospheric air by enclosing a bubble under the bodies, where 

 it looks like a globe of quicksilver as they swim about. As this 

 species is not only handsome but harmless, it is in great favour 

 with the keepers of aquariums, and is in consequence quite 

 scarce in many places where it used to be plentifttl, the 

 professional dealers having ransacked all the streams within 

 •easy reach of London. 



The family next in order, the Sphoeridiidse, are distinguished 

 from the preceding family by the shape of the tarsi, which are 

 not fitted for swimming, and the hinder pairs of which members 

 have the first joint much longer than the others. They are all 

 •small Liasects, rather globular in form, from which peculiaritv 



