174 MEDICAL ENTOMOLOGY 



substance. They hatch in about three or four days, according to 

 the temperature. The larvae at once attach themselves to the support 

 by their posterior suckers, and can be seen waving about in the 

 water. 



The body of the larva is cylindrical, gradually broadening out pos- 

 teriorly in the shape of an Indian club ; in some species the increase 

 in breadth is very gradual, while in others it is some- 



what abru Pt> and thus g ives the bod >' a constricted 

 appearance in the middle third. The colour varies 

 somewhat, dark olive green being the predominant shade, and the 

 one which harmonizes best with the leaf or other support to which 

 the larva is fixed. The body is composed of twelve rather indistinct seg- 

 ments, five of which usually form the dilated posterior end. On the 

 ventral surface of the first thoracic segment there is a well developed 

 fonvardly-directed pseudopod, which represents two legs fused to- 

 gether ; it is conical in shape, and is armed at its apex with a circu- 

 lar row of short hooklets or spines. When the larva is touched the 

 anterior pseudopod retracts. 



On the last segment there is another pair of pseudopods joined to- 

 gether to form a flattened, sub-cylindrical sucker, armed with a row or 

 rows of hooklets arranged in regular transverse series. True stigmata 

 are wanting ; the tracheal tubes end on the ventral side of the suckers, 

 where they join three short, cylindrical tentacles, the anal gills ; these 

 finger-like processes, which may be simple or branched, can be retract- 

 ed, but when it dies in still water, or when the larva is dropped 

 into spirit, they are always extruded. The head is large, somewhat flat- 

 tened, and almost rectangular in shape, with two black approximated 

 lateral eye spots, the anterior of which is usually the smaller of the two ; 

 the posterior is reniform in shape. The labium is broadly rounded off in 

 front ; the antennae are long and attenuated, and consist of three joints. 

 The first is very small and inconspicuous ; the middle, which is longer, is 

 about half the length of the last. Situated directly behind the an- 

 tennae there are two broad, somewhat flat arm-like processes, the 

 feeding brushes, each furnished with a long fan-like fringe of dark 

 hairs ; if the larva is examined with a lens when under the water, 

 they can be seen to open and close in rapid succession, the long 

 hairs whirling round and drawing in small objects towards the oral 

 opening. When the larva is dropped into spirit, they spread out and 

 can then be easily studied. 



The mandibles are stout blades of chitin, armed with short stiff 



