and extend their bodies to their full length ; they then measure '32 mm. 

 The young larvae remain for some time within the gelatinous envelope 

 of the egg-mass, and seem to feed upon its substance and upon 

 organic particles which are generally found attached to its outer surface, 

 but by the end of the second day they have for the most part 

 dispersed, and henceforth live independent and solitary lives each 

 within its mud-built tube. 



THE ANATOMY OF THE LARVA. 



The full grown larva is about 4*2 mm. long. The colour of the 

 body is pale green tinged with orange, with the exception of the 

 first three segments which are violet. The head is almost an opaque 

 brown, but the body is transparent, though not equalling in this 

 respect some other species I have met with. One larva specially must 

 be mentioned ; this species (No. 18 of Appendix) is also common in 

 the Yealm, and vies with the "Phantom Larva" (Corethra) as regards 

 transparency, so that, in elucidating the more obscure details in the 

 anatomy of C. piisio, such for instance as the distribution of the nerves, 

 I have found comparison with this species of great help. I have not 

 come across any larva nearly as suitable for microscopical examination 

 as this one ; and although found in a swift river it thrives very well 

 in the ordinary still-water aquarium. 



The larva of C. piisio is composed of a head and twelve segments, Segments of 

 and most probably, as we shall see later, a rudimentary thirteenth. y ' 



The first three segments, which go to form the thorax of the fly, are 

 easily distinguished from the rest by their violet colour and rectangular 

 shape, segment 3 being the shortest in the body. Segments 4-10 are 

 barrel-shaped, while the remaining segments bulge very little if at all. 

 Segment i bears a pair of prothoracic appendages each of which is 

 thickly covered with fine curved claws capable of being completely 

 withdrawn into the appendage. The last segment bears a similar pair 

 of appendages, the anal feet, which are longer, and bear fewer but 

 much stouter hooks ; the hooks in both cases are amber-coloured. 

 Among the different species I have found very little variation in the 



