190 INSECT TRANSFORMATION 



emphasize the fact that insects even though they live in water 

 belong essentially to the air, and most of them can, on 

 occasion, rise from their watery homes and indulge in flights 

 of considerable extent. 



But in the dragon-flies and mayflies we have to do with 

 insects that are typically aerial in the winged state, while their 

 larval and nymphal stages are aquatic. These growing forms 

 have, as we have seen, some provision for breathing the air 

 dissolved in water the mayfly grubs by their paired series 

 of abdominal appendicular gills, the dragon-fly larvae by the 

 network of air-tubes branching over the thin wall of the hind- 

 intestine or by the terminal gills modified from the tail ap- 

 pendages. Such modifications of insect larvae for aquatic 

 life 1 may be seen in different families and orders ; reference 

 has already been made to the stone-flies (Plecoptera) whose 

 larvae (see pp. 76-7) have tufted thoracic gills and to the caddis- 

 flies (Trichoptera) whose well-known case-inhabiting grubs 

 (see pp. 121-3) have thread-like abdominal gills. Many 

 examples of similar larval adaptation for life under water are 

 afforded by certain families of the Diptera, and to these 

 attention may now be profitably directed. 



The delicate midges of the genus Chironomus 2 often fly in 

 swarms on summer evenings in the neighbourhood of water ; 

 they have relatively long legs and abdomen, and the males 

 possess beautifully plumose feelers. The female, distinguished 

 by much simpler feelers, lays in water numerous eggs embedded 

 in a gelatinous substance which assumes the form of a long 

 string or cord ; the eggs lie in a tube which runs a spiral course 

 near the surface of this gelatinous cord, and they may approach 

 a thousand in number in one laying. The larva of a Chirono- 

 mus (Fig. 100 b) is a narrowly elongate grub, its distinct head 

 bearing short segmented feelers and strong toothed mandibles 

 which work obliquely backwards, not transversely across the 

 mouth. The first thoracic and the last abdominal segments 

 bear each a pair of hooked prolegs, and the special breathing- 

 organs are found on the last and the penultimate abdominal 



1 L. C. Miall : " The Natural History of Aquatic Insects ". London, 

 1895- 



2 L. C. Miall and A. R. Hammond : " The Harlequin Fly ". London, 

 1900. J. G. Needham and others: "Mayflies and Midges of New York". 

 Albany, New York, 1905. 



