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



water to flow through the case from the head end. The undulations begin at 

 the second abdominal segment and pass backwards to the tail end just as a 

 )iece of string which is fixed at one end and waved up and down at the other. 

 The rest of the body is kept steady so that the stream of water has a free 

 admission. This seems to be effected by the lateral process of the first abdo- 

 minal segment which can be pressed against the sides of the case and kept 

 from slipping by the spines which cover their points." 



Again, the same gentleman quoting Dr, Schmidt-Schmedt says — " The 

 larva moves its abdomen up and down most probably to renew the water 

 which bathes its body, and that the fringed sides (which Reamur supposed to 

 be an analogy with the gills of fishes) by increasing the breadth of the abdo- 

 men, add to the effect." It is just possible too Caddis larvae are able to store 

 up air by means of the silken covering, in the same manner that certain aquatic 

 caterpillars (^Hydrocampa) do which also form a silken covering, and like the 

 Caddis larvae are completely submerged and carry on respiration entirely by 

 means of stored air. Aquatic spiders are able to breathe when submerged by 

 carrying bubbles of air down with them entangled in the fine hairs covering 

 the body. 



The breathing of a water beetle {Dytiscus) larva offers a contrast to that of 

 a Caddis lai'va, Larvte of aquatic beetles must come to the surface to breathe. 

 The tail end of the body is thrust above the surface and air absorbed from the 

 atmosphere by means of two tracheal trunks, one in each appendage, these 

 trunks being continuous with two air vessels running longitudinally throughout 

 the length of the body and branching off into trachese to each segment. An 

 adult water beetle breathes very much in the same way, the body being 

 lighter than the water rises to the surface when the insect ceases its exertions 

 beneath the surface. The end of the abdomen is thrust above and the wing 

 cases raised to admit air bubbles which are lodged between the wing cases and 

 the back of the abdomen and kept there by a quantity of soft hairs, the air 

 being absorbed by the spiracles. Around the spiracles of some Dytiscid beetles 

 are certain cells which bear a close analogy with those of plants. A quantity 

 of air may be stored up at one time which passes from the lower spiracles to 

 the front ones. The hinder end of the body of an aquatic beetle is consider- 

 ably lighter than the fore-end, and this can be seen easily in the family 

 Dytiscid a when any members of it are confined in a glass vessel. They Avill 

 then be seen to swim nearly always in a horizontal position, rarely a lateral 

 one, and the tail end alwayr^ pointing to the surface of the water. The respii-a- 

 tion of the larva of a gnat or mosquito is effected in the same way as that of a 

 water beetle larva, and this manner of breathing is a distinct advantage to 

 both insects. The early lives of both water beetle and gnat are principally 

 spent in either feeding or searching for food, and as this is always obtained 

 beneath the surface of the water both insects have to be always on the look 

 out for it, and must therefore have their heads submerged so that no time may be 

 wasted betA^een their search and acts of respiration. The larva of a gnat is 



