LARVA OF THE GLOW-WORM. 81 



Viewed from the side, this organ is slightly curved upwards 

 at the tip, and ventrally the surface is entire. On the dorsal 

 side, however, there is a distinct groove (gr.) which fits the cor- 

 responding ridge on the labrum ; the edge of the groove is 

 strengthened by a thicker band of hairs. The hairs at the apex 

 of the hypopharynx are longer than the others, and are frequently 

 forked. 



Interrelations of Mouth-parts. 



The arrangement of the mouth-parts is such that it prevents 

 any solid matter from entering the gullet. This is effected by the 

 enormous number of hairs that surround the mouth, all pointing- 

 outwards, so that although the mouth is always open it is 

 impossible for any solid particles to enter. 



A comparison might be made here between this larva and the 

 larva of Dytiscus, which also sucks the juices of its prey. The 

 Dytiscus larva has its mandibles tubular, but the mouth can be 

 closed by an apparatus which has been described as a " mouth 

 lock," which automatically closes up the aperture when the man- 

 dibles shut. The larva pierces its prey with its mandibles, closes 

 them, and proceeds to suck the juices through the mandible-tubes 

 by means of the pharyngeal pump. When the mandibles open it 

 can swallow small particles in the ordinary way*. 



The Pharynx. 



The floor and sides of the anterior end of the pharynx are 

 strongly chitinised (fig. 8, ph.), and the tongue is a direct con- 

 tinuation of the floor. The sides at this point receive an 

 additional support from the chitinous fork which protrudes from 

 the posterior end of the labrum (fig. 6, c.f.). More posteriorly, the 

 chitinous fork ends and the sides and floor of the pharynx become 

 membranous, the chitin tapering down to a narrow ventral strip. 

 The roof of the pharynx up to this point is also membranous, but 

 here it turns sharply upwards and forms a small vertical chitinous 

 plate (figs. 1 & 8, c.p.), from which muscles (fig. 8, d.m.) run to the 

 dorsal integument of the head. From the apex of this plate 

 another larger one slopes downwards (fig. 8, c.p.'), and runs into 

 the dorsal surface of the oesophagus. Two strong bands of muscle 

 (figs. 1 & 8, p.m.) are attached to the posterior surface of this plate, 

 and run to the back of the larva's head ; while from its edges 

 bands of muscle (fig. 8, l.m.) run down on either side of the 

 pharynx and are attached to the posterior end of the plate forming- 

 its floor. This plate is perforated by two pairs of small holes, the 

 function of which I cannot ascertain at present. 



This apparatus evidently forms a suction-pump, and is worked 

 by contraction of the muscles attached to the two dorsal plates, 

 which raises them and makes a vacuum into which the liquid 

 food flows, while contraction of the lateral descending muscles 



* L. C. Miall, ' The Natural History of Aquatic Insects,' 1912, p. 44. 



Proc. Zool. Soc— 1915, No. VI. 6 



