310 Transactions. — Zoology. 



The black claws are not arranged in circles, as they are in 

 Eristalis, but in irregular groups, and the number differs in the 

 different segments. 



The first segment is armed on the ventral surface with a series 

 of closely set black rectangular plates, each toothed along its 

 hinder margin ; these plates are in about half a dozen transverse 

 rows, each row shorter than the preceding, giving rise to a some- 

 what triangular black patch. The anterior edge of this and of 

 the second segment is also armed with a row of short black 

 conical tooth-like spines. 



The " head " bears on either side a small triramous organ, each 

 branch of which is somewhat dilated at its extremity, and is 

 apparently perforated by a minute aperture. Each is traversed 

 by a brownish granular canal (in which I could not detect any 

 rings), which at the base of the organ unites with the other two to 

 form a single canal, which runs backwards for a short distance, 

 then, near the hinder end of the head, dilates to form a hemi- 

 spherical or conical saccule, which rests against and is partly 

 embraced by a dilated tracheal tube, colourless and distinctly 

 ringed as usual ; from this p. trachea can be traced backwards 

 into the body. This appears to be an " anterior spiracle " such 

 as occurs in the pupa of several aquatic Diptera, such as the 

 gnats and Eristalis, though in form it does not resemble the 

 organ in the latter fly. 



From each of the posterior spiracles, situated at the tip of 

 each of the forks of the tail, a trachea can be traced forwards 

 into the body, and there is no dilatation except the small one 

 just referred to. 



The Larva. 



Amongst the dark-brown " puparia " I find one individual 

 which is grey in colour, with a softer and flatter body ; the 

 spines covering the body are much longer than in the puparium ; 

 each of the ventral paired groups of "claws" is on a distinct 

 prominence or transverse ridge, which appears to represent the 

 paired " legs " of Eristalis, the ridge of segment 10 being more 

 prominent than the rest. Further, round each segment, as well 

 as on the " head," is a series of tufts of small pale hairs, no doubt 

 sensory in function. Each tuft consists of three hairs rising 

 apparently from a common base ; they are colourless, and much 

 longer than the spines. These sensory hairs are also observable 

 on the puparium, but are less conspicuous. The anterior end 

 bears a pair of dorsal " eye-spots." The mouth is armed on 

 each side with two or three rows of stout spines, and within the 

 cavity is a pair of short antenna? ; each appears to be 3-jointed, 

 the terminal joint being brown, and to spring from a circular 



