BIOLOGY AND STRUCTURE OF HYDROPHILUS CARABOIDES 651 



long sensory hairs of the larva it becomes its prey, as it gets very 

 little chance of escaping the murderons mandibles ; in this 

 latter case the sensory hairs attend indirectly the feeding 

 wants of the larva. 



The sensory hairs of the pleural appendages are of consider- 

 able length ; in the young larva of the first stage the hair 

 might be twice or thrice as long as the pleural appendage. 

 In consequence the receiving surface of the body of the larva 

 is considerably increased, and the latter is able to orientate 

 itself better in the surrounding medium, both for taking 

 measures of defence and for the capture of prey. The armature 

 of the head of the larva is usually kept in readiness, i. e. all 

 oral appendages are wide open and have only to contract at 

 the suitable moment. 



An analogous sensibility is found also in the hairs on the 

 tergites of the body. When the irritation comes from above, 

 the larva throws its head up and backwards with the same 

 quickness and generally attains its end. 



But the larvae of H. caraboides are not absolutely 

 safe from peril. For instance, they are ready to devour 

 each other if kept in close vials and fed unsatisfactorily. An 

 examination of the skins of devoured larvae showed that they 

 were all wounded in the tergites of the thorax only. This 

 place is, so to say, the Achilles-tendon of our larvae. 



The thoracic integuments are also not devoid of sensibility ; 

 but if the attacking animal succeeds in seizing it at once by the 

 tergites of the thorax, the larva of H. caraboides finds 

 itself in a defenceless position, because in this case it cannot 

 throw back its head and put its mandibles into action. 



In some of the larvae the pleural appendages and their 

 terminal hairs were partly torn off. The aperture of the 

 wounded places were shut by dark-coloured chitinous plugs 

 of an evidently inflammatory origin. Doubtless the respective 

 larvae had been in a position endangering their lives, and they 

 had come out safely thanks to their sensory and tactile 

 apparatus, a partial loss of which is not fatal. 



After these biological remarks we shall discuss the structure 



