BLOOD-SUCKING NEMATOCERA : SIMULTIDiE 125 



submerged stones and water-weeds, and the larvae are 

 aquatic. So far as is known the larvae can live only in the 

 well-aerated — though not necessarily clean — water of rapid 

 streams. Larvae of one of the common British species, 

 removed from their natural habitat and kept with proper 

 care in an aquarium, will live for a few days, but they eventu- 

 ally die with their gills extruded, which is fair evidence of 

 asphyxia. 



The larva (Fig. 31) is composed of 12 not very well- 

 defined segments besides the head, and is shaped something 

 like a slender flask, its after part being moderately inflated. 

 The well-chitinised head, in addition to two pairs of eye- 

 spots, a pair of antennae, and mouth-parts formed for biting, 

 carries a pair of large and particularly elegant mouth-fans, 

 each of which is composed of a row of about fifty long and 

 regular filaments articulated to a stout flexile stalk ; these 

 are used for sweeping food towards the mouth. On the 

 ventral surface of the ist segment of the fleshy body there 

 is a stumpy leg (formed of a pair of fused appendages) 

 crowned with booklets, and at the end of the last segment 

 there is an elegantly burred sucker (also formed of a 

 pair of modified appendages) ; these are used for creeping, 

 after the manner of a leech, but the front foot is also used 

 for fashioning the silky secretion of the salivary glands, and 

 for pushing food towards the mouth, and the sucker is a 

 very necessary organ of attachment, one of the most 

 characteristic attitudes of the larva being to sit upright on 

 the end of its tail — to use the language of the poets of the 

 daily press — with its mouth-fans standing out from its head 

 like a pair of shaggy ears. The larva possesses a pair of 

 extremely long tubular salivary glands (Fig. 31), which are 

 used for spinning anchoring-threads and life-lines — an adap- 

 tation, like the sucker, for life in turbulent waters. Judging 

 from the contents of the alimentary canal, which runs straight 

 through the body (Fig. 31), the larvs live on microscopic 

 vegetation, but they can often be observed, as they sit 

 together in crowds, pecking at passing larvae of other kinds 

 and sparring one with another. According to Mia 11 the 

 tracheal tubes are large and give off a network of fine 

 branches to the skin ; but in one very common British 



