and Life History of Psychoda sexpunctata. 297 



of the mouth-appendages, which are rapidly extended and 

 closed, so as to scrape the bottom. 



The head (Fig. 2) is subcorneal, much reduced, and 

 partly retractile. It can be withdrawn into the prothorax, 

 so that the head is concealed as far forward as the eyes. 

 This position is temporarily assumed during crawling, and 

 is normal in larvae about to pupate. The head nearly 

 resembles that of Pericoma* and Maruina.f In each case 

 the mid-dorsal surface is occupied by the roughly triangular 

 clypeus, flanked on either side by the large epicranial 

 plates, which bear the black, shining, simple eyes, and the 

 antennae. The antennae are even more reduced than in 

 Pericoma, and are little more than knobs. The forward 

 prolongation of the clypeus is the labrum. This is an 

 elongated triangular organ ; its apex is turned underneath 

 in such a way that the tip lies almost directly beneath its 

 junction with the clypeus. A few hairs arise from its 

 anterior edges, and on the surface of the apical part, which 

 is morphologically dorsal, but actually ventral, there occur 

 a large number of backward-directed spines. On each 

 side of, and immediately behind the labium is an appen- 

 dage, probably the mandible, which is short, and ends 

 bluntly. From each appendage arise two large plumose 

 setae, one running forward, the other outward. There are 

 also two bunches of shorter setae. Immediately behind the 

 supposed mandibles is a pair of semi-circular, plate-like 

 appendages, which probably represent the maxillae. 

 Between them and in the median line is a comb-like 

 organ with its teeth projecting forwards. A similar plate 

 is common in Nemoceran larvae, and has been identified 

 with the submentum.t 



Nervous System of the Larva. 



The nervous system (Fig. 3) consists of the usual cere- 

 bral ganglia and the ventral chain. The cerebral ganglia 

 are pear-shaped, and from their pointed ends arise a pair 

 of nerves, which run forwards into the head. The sub- 

 cesophageal ganglia are, as usual, connected with the 

 cerebral so as to form a ring round the oesophagus, through 

 which runs the dorsal vessel. Behind these is a series of 



* Miall and Walker (1895). f M tiller (1895). 



+ Miall and Hammond (1892 and 1900). 



