82 ON THE LARVA OF THE GLOW-WORM. 



lowers the roof again. A similar contrivance is found in some 

 groups of Hemiptera*, only in them there are no ventral muscles, 

 the roof falling back into its place by the natural elasticity of the 

 pharynx. 



The method of feeding of this larva is obviously different from 

 that of the Dytiscus larva, for it has no means of shutting its 

 mouth, and hence cannot suck through the mandible-tubes only. 

 The mouth, although guarded by an immense number of out- 

 wardly directed bristles, has sufficient aperture to allow of the 

 passage of a fine hair ; this, if placed on the tip of the hypo- 

 pharynx and pushed gently along, runs down into the pharynx. 

 On the other hand, a hair pushed down the mandible-tube bends 

 forwards and curves out again at the mouth ; this is difficult to 

 understand unless it is due to the forwardly directed hairs that 

 lie on the base of the mandible. A stiffer bristle might overcome 

 this resistance, but I could not insert one into the tube ; it is 

 probable that liquid, such as would be sucked up through the 

 mandible, would trickle through the hairs and be drawn into the 

 pharynx by the action of the suction-pump. 



It is clear, at any rate, that no large particles of food can find 

 their way through the mass of hairs that surround the mouth ; 

 they are are all strained off and removed later by the terminal 

 adhesive organs. It is probably the difficulty of extracting these 

 particles that causes the larva to continue to cleanse itself long 

 after the apparent need for it is over. 



EXPLANATION OP THE PLATE. 



Lettering. 



a.c, articulation for condyle of mandible ; ant., antenna ; a.op., anterior opening of 

 canal through mandible; art., articulation of hypopharynx ; br., brush of hairs on 

 mandible ; c, condyle of mandible ; cd., cardo ; c.f., chitinous fork ; c.p., chitinous 

 plate of pharynx ; c.p.', posterior chitinous plate ; d.m., dorsal pharyngeal muscle ; 

 .?«., galea ; gr., groove of hypopharynx ; hyp., hypopbarynx ; la., lacinia ; 

 Ibr., labrum ; la.p., labial palp; l.m., lateral pharyngeal muscle; md., mandible; 

 m.r., mid-rib of labrum; int., mentum; mx.p., maxillary palp; ces., ossophagus ; 

 op., opening into gullet ; ph., chitinous floor of pharynx ; p.m., posterior pharyngeal 

 muscle ; p.op., posterior opening of canal through mandible; ptli., prothorax 

 sm., submentum ; st., stipes ; t., tooth on mandible. 



The figures, with exception of fig. 8, were all drawn with a camera lucida. 



Fig. 1. Dorsal view of the head of a larva (X 16). The prothorax has been cut 

 away to expose it, and the dorsal integument removed. 



2. Dorsal view of right mandible. (X 30.) 



3. Dorsal view of left mandible. (X 30.) 



4. Dorsal view of first maxilhe and labium (X 30). (Note asymmetrical 



sclerites.) 



5. Ventral view of first maxillae and labium. (X 30.) 



6. Ventral view of labrum. (X 30.) 



7. Dorsal view of hypopharynx. (X 30.) 



8. Diagram of the pharyngeal pump. 



* P. Muir and J.C.Kershaw, "On the Homologies of the Mouth-parts of 

 Hemiptera," Psyche, vol. xviii. no. 1, 1911, p. 5. 



