740 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XIX. 



or descends in a complete circle. This is easily observed if some gnat pupse 

 be confined in a glass of clear water. 



The hairs of aquatic insects and their probable uses form an interesting 

 study in themselves. These may be divided into five classes : — 



(1) Those that aid respiration. 



(2) Those that aid feeding. 



(3) Those that aid swimming. 



(4) Those that serve for protection. 



(5) Those that act as organs of perception. 



(1) Situated near the spiracles of a Dytiscid beetle are a number of stifl: 

 hairs, which when viewed under the high power of a microscope present an 

 appearance of pin-like structures the head of the pin fixing the hairs to the 

 body. These hairs entangle the air bubbles and moreover, prevent water from 

 getting into the spiracles and also serve to keep the wings dry. In some of the 

 aquatic Rhyncliota (Notonectidcc) the hinder abdominal spiracles are very small 

 and near these are tufts of hair which entangle air bubbles and serve to protect 

 as well the spiracles. " Lai-ger spiracles, well defended by hairs to prevent the 

 accidental entrance of water, are found on the sides of the thorax. To these 

 the air is led by a singular passage. The side of the body which floats uppermost 

 is keeled along the middle line. On each side of the keel and between it and 

 the lateral edge runs a long row of elastic hairs, while a second and parallel 

 row runs along the edge itself. These roAvs of hairs enclose a watertight 

 covered way leading to the thorax, and along it the air is guided to the large 

 thoracic spiracles."^ 



(2) All Dytiscid beetles are highly carnivorous, feeding on other animals and 

 the juices of their victims.* On the inner side of the maxillae of a Dytiscid 

 beetle are ranged a row of stiff inward curving hairs. These, I think, serve as 

 strainers, allowing an inflow of the juices into the mouth and keeping out foreign 

 matter that would otherwise choke the insect. One of the aquatic Diptera larva 

 {Corethra) has curious shaped mandibles which consist of five slightly curved 

 teeth. The antenna of this larva is prehensible and serves not as an organ of 

 touch but for the capture of prey such as minute crustaceans, etc. The 

 captured prey is crushed by the mandibles and forced into the mouth not 

 however to be swallowed. At the back of the mouth there are a iiumber of 

 stout hairs. These hairs allow no ingress, so that the body of the victim is 

 digested in the mouth by the action of the salivary glands and only the juices 

 flow into the stomach. Here again is another instance of a straining apparatus. 



(3) It was shewn in the former part of this paper how certain hairs aid 

 many aquatic insects in swimming. In the Dytiscido' these are arranged mostly 

 on the inward sides of the hind limbs in a close set fringe. On the outer sides 

 are rows of stiff, sharp bristles. In some of the Rhyncliota {^otonecta) both hind 

 limbs are heavily fringed with fine hairs. On each side of the swimming organ 



1 Miall " Aquatic Insects." 



* I once watched a Dytisms suck a large earthworm until nothing remained but the skin 



