762 Mr. Frank Balfour Browne [May 9, 



The larvse of Hyilrocharis, like those of the Jji/liarus, will eat 

 almost any kind of animal matter, and hence they are easily sup[)lied. 

 1 fed them mostly upon chopped worms, but their method of feeding- 

 is very different from that of the DyUscus. They seize their food 

 with the jaws, antennas, and the other mouth parts, and they then 

 come to the surface, and, raising their heads and part of the body out 

 of the water, they proceed to chew up the food by opening and 

 closing the jaws, turning it from time to time with the other mouth 

 parts. The jaws are not perforated, nor is there any mouth-lock as 

 in DyUscus, and they suck in the juices of the prey by the mouth, 

 spittnig up saliva at intervals, which actually froths over the food and 

 digests" it, the dissolved material then being sucked down. The 

 external digestion is so complete that in the case of a thick piece of 

 worm all that is ultimately rejected is the thin transparent outer 

 pellicle. 



In the mouth parts of the larva I want to draw your attention to 

 a curious want of bilateral symmetry, noticeable not only in the jaws 

 — one of which, the left, has a small extra tooth near its base — but 

 also in the upper lip. In many species there is an absence of bilateral 

 symmetry where a pair of organs are complementary. Thus in the 

 jaws of the beetle itself, the base of the left one is hollowed out to 

 receive the base of the right one, which is convex, the two being 

 related as pestle and mortar for grinding up the food. The larva 

 of another species of the same group also shows asymmetry of the 

 jaws, but here again it is definitely associated with the method of 

 feeding. This species feeds upon pond snails, and the left jaw holds 

 the shell while the right jaw with its large double tooth cuts 

 through it. 



The asymmetry of the upper lip, however, is at present inexplicable, 

 and curiously enough it occurs in several other species. 



The larva of Hydrocliaris, like that of DyUscus, passes through 

 three stages, the first two of which occupy from five to eight days, 

 and the third stage, up to the time the larva is full grown, occupies 

 about four weeks. It then leaves the water and burrows into the 

 earth, forming a cell just as the DyUscus larva did. I bad many 

 specimens of these larvaj, and so made many experiments with them, 

 and one curious fact about them is that the instinct wliich leads 

 them to burrow into the ground and make a pupal cell only lasts 

 for one or, at most, two days. In no case, where I removed a larva 

 even immediately after the completion of its cell, did it make any 

 attempt to form another one, and if left on the surface of the soil 

 it moved about listlessly and ultimately died, apparently of drought, 

 since if placed in a damp position, for instance, in an artificial cell 

 it survived and pupated. If a cell was damaged before completion 

 the larva often completely destroyed it, apparently in the attemjit to 

 repair the damage, ami w'ould be found sitting amongst the ruins. 

 Once the cell is completed the larva rests for about three weeks. 



