204 Life History of Wireworms 



angle with the inner edge of the mandible at the point of junction, and 

 projects in the horizontal plane. 



The second denticle, also on the inner face of the mandible, is situated 

 nearer to the base. It is much sharper than the first and is on a plane 

 nearer to the ventral surface of the mandible, arising from a point a 

 little within the actual margin. This denticle is called by Schiodte the 

 retinaculu7n and is common to all the Elaterid larvae known with the 

 exception of the section Agripnini (of which Brachylacon murinus, L. 

 is our only British species) and the genus Cardiophorus. 



At the base of the inner edge of the mandible there arises a small 

 process of brush-like structure called by Schiodte and Henriksen the 

 'penicillus. Ford, who gives a figure of the mandible (5), has called this 

 process the "lacinia mobihs," but it is certainly not homologous with 

 the lacinia mobilis of some of the Malacostraca, to which the term was 

 first appHed. In them, as Mr L. Borradaile has kindly pointed out to 

 me, the process is independently moveable, whereas the process in 

 Agriotes is fixed. Its function seems to be to cooperate with the rest of 

 the dense mass of hairs at the entrance to the mouth in preventing the 

 entrance of unwholesome matter to the mouth. Schiodte, however, 

 refers to it as assisting in the absorption of blood. Several hair folhcles 

 are visible on an examination of the dorsal surface of the mandible, of 

 which one is situated about in a fine with the retinaculum and almost on 

 the outer margin of the mandible : two others are situated nearly in the 

 median line, more basally. The first of these bears a seta of considerable 

 length, which extends obhquely forwards and doubtless has a tactile 

 function. 



The mandible itself is of considerable thickness and somewhat ex- 

 cavate on its outer side, but is narrowed on the inner side to form the 

 cutting margin. In transverse section it is therefore almost triangular. 

 Much variation appears to exist in the mandibles of this species, but 

 some of the apparent variation is caused by erosion, mandibles which 

 should normally be sharp-pointed and somewhat long presenting an 

 appearance of stumpy bluntness. 



The principal condyle is ventral and articulates with the thickened 

 anterior margin of the epicranial plate, ventral to the base of the antenna. 



Between the mandibles, at the anterior margin of the compound 

 structure which has been called the cephahc plate, there is a thickening 

 of the chitin into a tridental process, of which the middle denticle is the 

 longest (Fig. 2 6). This process is situated immediately above the entrance 

 to the mouth and was referred to by the older writers as the clypeus, but 



