Manchester Memoirs, Vol. hi. (191 2), No. 11. 3 



mechanism {Fig. i, r) and can be regarded as somewhat 

 produced angles of the mouth cavity. 



For some little distance the ventral wall of the duct 

 leading away from the base of the mandible is formed 

 by a strong process, which with a little pressure can be 

 bent forwards {Fig. i, .r). However, it is never everted 

 naturally, as there is no joint at its base, and the ventral 

 interlocking ridge {Fig. i, r) of the mouth is continued 

 without interruption along its antero-superior border. J 

 regard each of these structures {Fig. \,x) as a modification 

 of a free anteriorly directed process, and by reason of 

 their position with respect to the mandibles and maxillae, 

 I am inclined to include them with those similarly situated 

 processes found in apterygote and in certain of the more 

 primitive winged insects, and variously referred to as 

 '' superlingNcE" (Folsom) or '' maxil/iclce" (Hansen). Each 

 of these possible maxillulai is a simple, well chitinised, 

 acute, three-sided process, with one border, as has been 

 mentioned, adapted to interlock with the ridge on the 

 upper lip. These parts were not materially different in a 

 young larva under three-quarters of an inch in length. 



An examination of four species of dytiscid larva, all 

 of which could be referred with more or less certainty to 

 the genus Ilybiv.s, revealed the existence, in these species 

 also, of certain structures comparable to maxillula.'. These 

 were soft lobes {Fig. 2, x) which, present one on each side 

 of the hypopharynx, normally reposed against slight 

 depressions on the inner side and at the base of the 

 mandibles. Each was a delicate, conical process, some- 

 what shrunken, or even collapsed, in preserved specimens. 

 In these larvae the mouth is not so perfectly closed as in 

 Dytiscits, and it is not unlikely that the foregoing process 

 represents the earlier condition of the maxillular structure 

 described in Dytisciis, the strengthening and lateral 



