ADAPTATIONS TO HAUNTS AND SEASONS 277 



water to feed between leaves or on stems. The larvae of 

 Haemonia feed on Potamogeton. 



The grubs of these beetles are soft-coated and thick in 

 the middle of the abdomen, tapering towards the head and 

 tail ends ; on the thorax are three pairs of short jointed legs. 

 So far the grub resembles many of the vast host of leaf- 

 beetle larvae that feed on land plants, but the stout biting 

 mandibles have no grinding area. The maxillae are remark- 

 able in having the inner lobe (lacinia) modified into a strong 

 piercer (Fig. 69, E,/) partly sheathed by the delicate sub- tubular 

 outer lobe (galea). When the grubs are feeding, not the 

 head only but the greater part of the thorax also, is imbedded 

 in the plant-tissue. From his examination of the jaws and 

 the contents of the food-canal, Boving concludes that 

 these grubs bite the plants in order to obtain and suck sap ; 

 they do not swallow solid pieces of tissue. 



Living submerged for several months, probably more 

 than a year, the Donaciine larvae require some provision for 

 breathing. It is well known that the great majority of 

 aquatic insect grubs breathe in one of two ways. Many of 

 them get continual or intermittent contact with the upper 

 atmosphere, usually by thrusting through the surface film 

 an outgrowth or processes at the tail-end of the body, 

 directly continuous with the spiracular and air-tube system 

 as in the case of the gnat-larva (Culex) and the rat-tailed 

 maggot of the drone-fly (Eristalis), or affording a channel 

 by means of which air can reach the protected spiracles as 

 in the case of the large carnivorous water-beetles (Dyticus) 

 and the water-scorpion (Nepa). Many others make use 

 of the air dissolved in the water by means of various types 

 of tracheal gills, like those of the slender dragon-flies 

 (Agrionidae or damsel-flies) and the mayflies ; or blood- 

 gills like those of the caddis-larvae and the grubs of midges 

 belonging to various families of Diptera. 



The adaptation of the Donaciine larvae is especially 

 remarkable because they make use of atmospheric air which 

 they seek not above the surface-film but enclosed in the 

 tissues of submerged water-plants. It has been mentioned 



