SPECIES OF BRITISH HYDROPHILUS. 73 



since they were done, they are as perfect as when they 

 were first prepared. This method, however, will not 

 retain them so permanently as when they are mounted in 

 Canada balsam, between two slips of glass, in which case 

 the specimens may also be of much larger dimensions. 



The manner in which this larva treats its prey evinces 

 an extraordinary degree of instinct. Many of the crea- 

 tures on which it feeds are crustaceous about the head 

 and back ; hence they are most vulnerable at the under 

 part of the body. This part, therefore, the larva attacks ; 

 and, to accomplish its aim, swims underneath the in- 

 tended victim, and bending back its head, which is even 

 with the surface of its back, is enabled thus to reach its 

 prey by means of its jointed antennae. (See a, fig. 30, 

 which represents a magnified view of the larva taken 

 while young.) Its next operation is to pierce it with the 

 mandibles (b). Having thus secured its object, it im- 

 mediately ascends to the top of the water, and, holding it 

 above the surface, so as to prevent it struggling, shakes 

 it as a dog would a rat. The prey of this larva is often 

 larger than its destroyer. Its next operation is to insert 

 the piercer and sucker (d), which is capable of being 

 thrust out or withdrawn at pleasure. When the juices of 

 the victim are not easily procured by suction or exhaus- 

 tion, the serrated pair of forceps (c), is employed to tear 

 and masticate it, and thus cause the juices to be more 

 easily obtained. If its food be plentiful, this larva arrives 

 at its full growth in the course of three or four months, 

 and is then nearly opaque, and covered with hair. It can 



