454 ()R<;a\s <»i-" a xotonixtid. 



liairs, wliicli niCL-t >iinilar liairs ari--iiiK I'rdin the cor.nc-^i'uni edgy. I la re 

 is tlir.s formed a rhannel on each side of the ahdomen which is filled with 

 air. and in wliich the spiracles are placed. The insects hang in the water 

 abdomen up. witli its extremity just piercmg the surface film. In most 

 species tliere are tliree tufts of hair, which spread out on the surface, 

 leavirig an open, water-free spot in the middle which is the |)oint where 

 the ccnmection is made between tlie alidominal reservoirs and the atmos- 

 phere. When totally sul)merged. the opening closes in some way not well 

 explained so far. altliough tlie writer believes that the three tufts men- 

 tioned lap over, and in some manner serve to obstruct the entrance of 

 water into the channels. In any case these channels act as storage 

 reservoirs when the insect is in its element. The hairs are not set so 

 near together as to touch, but they are sufficiently close to form an aqueous 

 t'dm at a tension between them wdiich acts to retain the air in the chambers, 

 and at the same time to keep w.nter out. Very little seems to be known in 

 regard to their intern.nl respiratory system. It might seem, though, tliat it 

 should be- simjile. 'j^lu- iiym])lis are not diUercnl from tla- ;idult-' in this 

 ada])talion. 



In my Figure i. K is the keel hearing laterally projecting 

 hairs. P the pleurite or connexi\iuni. S the spiracles, and CH 

 the channel. The hairs are sho\vn on one side only. 



In my material the keel hecomes very flat as it proceeds 

 towards the head, and on the hasal somites of the ahdomen is 

 liardly reco,unisable as a keel. It is only on the two terminal 



somites that it is a true keel. The hairs on it, while longer than 

 tliose on the pleurite. are much fewer, and appear to play a small 

 role in maintaining the air in the channel. 



1 found a rather interesting prolongation of the channel 

 forwai'ds. As shown in my figure, the channel swerves distally 

 around the coxa of the hind limb. MTC. It ijasses forward 

 beneath a caudal prolongation of the meso.tlK)racis scutellum, 

 MSC. Near the coxa oi the mesothoracic limbs, MC, is a 

 spiracle undei* this jilate. I failed to find more than one thoracic 

 spiracle. I have indicated the swerving part of the channel 

 as CH. 



The channel which jjasses around the hind coxa also com- 

 municates with the space beneath the wings. FW and HW. In 

 life there is always a shiny film of air under the basal part of 

 the wings; this air does not extend very far caudally. This 

 would appear to form a supplementary reservoir of air. The 

 hairs on the distal edge of the mesotiioracic scutellum form a 

 seal again.st water over the point where the channel reaches the 

 edge of the wings. The hairs on the caudal part of the scutel- 



