292 THE BIOLOGY OF INSECTS 



clothes the rocks. The grub (Fig. 72, c) has a brown head 

 with obhquely set mandibles, and paired pro-legs with 

 circles of hooklets on the first thoracic and last abdominal 

 segments. In these characters it resembles closely the 

 ** bloodworm " larva of an ordinary freshwater Chironomus ; 

 but it needs no special blood-gills for respiration, breathing 

 all over the surface of its delicate and transparent body- 

 wall. Several shore-haunting Chironomidae from Samoa 

 have been recently described by F. W. Edwards and 

 P. A. Buxton (1926). These include a species of Clunio, 

 and a new type {Pontomyia natans) which is perhaps the 

 most remarkable of all marine Diptera. The male (Fig. 73) 

 has very long fore and hind legs, the wings reduced and 

 twisted, and the spiracles closed. This insect lives entirely 

 submerged, swimming at night with its long legs and 

 narrow wings and breathing through the delicate body- wall. 

 During daylight the midges are believed to hide in the 

 patches of Halophila, a pond-weed like plant that grows 

 in the Samoan kgoons. The female Pontomyia (Fig. 73, h) 

 is wingless like that of Clunio, but still more degenerate, 

 as fore-legs are quite absent and the others reduced to 

 tiny vestiges. Buxton believes that she spends her whole 

 Ufe in " the mud tubes among the leaves of the plant 

 Halophila, where the larvae and pupae are also found. 

 No other insect submarine in all its stages had been 

 previously observed. 



In our survey of examples of freshwater insects (pp. 281- 

 282) reference was made to several members of the 

 Hemiptera such as Gerris and Velia. These bugs have 

 relations living on the sea-shore or on the surface of the 

 estuaries and oceans, which are perhaps the most remarkable 

 of all marine insects as regards adaptation to their special 

 and unusual haunts. In some families a gradual transition 

 from terrestrial to salt-water surroundings may be traced. 

 The dull, ovate insects of the genus Salda, for example, 

 have some species frequenting dry heaths, others haunting 

 the edges of ponds and streams, others again living on salt 

 marshes or close to tidal waters. These are well able to 



