270 



Transactions. 



When viewed from the side a swelling is seen upon the ventral surface, 

 from which, at its base, arise numerous short and stiff bristle-like hairs 



(fig. 1, ds). Within the vesicle, 

 and completely filling it apically, 

 are a pair of large tracheae 

 (fig. 2). Arising from the trun- 

 cated apex, and apparently con- 

 nected with the tracheae are 

 a number — at least 3 — of tri- 

 angular structures bearing nu- 

 merous long and sinuated hair- 

 like appendages, each of which is broad and hollow (?) on the basal half 

 but terminates distally in a whip-like filament. 



The head — anterior process — is roughly triangular in profile, and bears 

 at the downcurved apex a rounded process beset with small hooked bristles 

 (fig. 3, a). When viewed from beneath, the head is dome-shaped (fig. 4), 



Fig. 2. — Apical tracheae. 



Fig. 3. — -Profile of head. 

 Fig. 4. — Head of larva, ventral view. 



with a large square notch on the anterior middle half, in which is seen the 

 apical process already referred to (fig. 3, a). This notched cavity is bounded 

 by a distinct ridge (fig. 4, r). The apical process (fig. 3, a) is now seen to 

 be more or less almond-shaped, its centre being occupied by a similarly 

 shaped cavity lined with delicate hairs (fig. 4, o). Separating this apical 

 structure from the margin of the square cavity is, on each side, a row of 

 3 contiguous cup-like depressions, the posterior ones being more or less 

 elongate (fig. 4, p). 



These larvae feed immersed, but for their posterior process, in the slush, 

 and are continually on the move. If disturbed they curl around any small 

 obstacle that may be handy, and remain quiescent till the disturbing 

 element is removed. The larval period extends into several weeks, but 

 the total number of moults is uncertain. 



The pupa rests embedded in the semi-liquid material on the surface of 

 the slush, its two spiracles free to the air. Its power of movement is 

 restricted, being able only to twist and twirl its abdomen to a slight 

 extent, and it is quite unable to swim or otherwise care for itself. 

 Like the larva, it varies in length, the longest being about \ in. In 

 colour it is yellowish-white ; in shape elongate, but broad and rounded 

 anteriorly, and narrowing considerably toward the terminal segment (fig. 5). 

 There are 9 segments, each connected by a membranous intersegmental 

 membrane, visible only when the bodv is fullv extended. Anteriorly is 



