158 Knapioeed Qall-flu 



of three short papillae joined together at the base ; a slightly elliptical 

 aperture is situated at the apex of each papilla, and these lead into the 

 spongy felted-chamber (Filzkammer) which is in communication with 

 the longitudinal canal. In some preparations I have been able to 

 distinguish a membrane between the inner boundary of the felted- 

 chamber and the longitudinal tracheal canal, and this is perforated 

 by a small aperture 4/x in diameter (Fig. 15). 



The posterior segment bears the anus and the posterior spiracles ; 

 it is wider on the ventral aspect, where the anus is situated in the mid- 

 ventral line, than on the dorsal and lateral aspects. A shallow horse- 

 shoe shaped depression is present on the posterior surface of this segment 

 at a short distance from its dorsal and lateral borders, and a slight 

 depression, situated just dorso-median to the posterior spiracles, is 

 also apparent. The surface is marked with a number of very fine grooves 

 or lines which run in various directions ; round the spiracles they are 

 arranged concentrically. A number of small darker-coloured areas may 

 be observed on various parts of this surface, particularly on the ventral 

 portion ; they indicate the points of attachment of muscles (Fig. 12). 



The posterior spiracles are situated slightly nearer the dorsal than 

 the ventral aspect, as in the larva of U . cardui, and they are about 0'7 mm. 

 apart. They are larger than the anterior spiracles and darker in colour ; 

 anatomically they are very similar to these but the apertures are more 

 definitely elliptical in shape and are arranged in a radiate manner. They 

 project very slightly from the body surface (Fig. 14). In one instance 

 a variation in the number of apertures in the left posterior spiracle of a 

 larva was noticed ; this spiracle possessed four apertures instead of the 

 usual number three. 



In concluding this description of the larva, the small number of 

 lobes or papillae of the anterior spiracles as compared with the number 

 on the anterior spiracles of many other Trypaneid larvae may be noted ; 

 Banks (1912) describes nine Trypetid (Trypaneid) larvae whose anterior 

 spiracles each bear a large number of lobes varying from about fifteen 

 in Ceratitis capitafa Wied. and Rhagolelis pomonella Walsh, to thirty-eight 

 lobes in Dacus fernigineus Fab. ; whereas in the larva of U. solstitialis 

 and U . cardui (Mik) three lobes only are borne on each anterior spiracle. 



