Manchester Me}]ioiys, Vol. Ivi. (19 12), No. 1|. 



XI. The presence of Maxillulae in Larvae of Dytiscidae. 



By Joseph Mangan, M.A., 



Lecturer in Eionoiiiic '/.oology in the University of Afanchester. 

 (Received and read April 2nd, igrs.) 



The DytiscidcX, a family of commonly occurring- 

 aquatic beetles of exceptional voracity in both the larval 

 and adult state, are of considerable general interest, 

 particularly owing to a singular adaptation of the mouth 

 parts, by which the larvae of these creatures are enabled 

 to suck the juices of their prey. It is the purpose of the 

 present communication to point to the existence, in the 

 mouth parts of some at least of these larvae, of a pair of 

 minute processes which are probably homologous with 

 the maxillulae, or rudimentary oral appendages, found in 

 certain primitive insects. 



The precise nature of the mouth opening of the larva 

 of Dytisciis Diarginalis, the most well-known member of 

 the group, hitherto a matter of conjecture, has recently 

 received detailed treatment at the hands of Rungius (1), 

 who points out that the entrance to the mouth remains 

 permanently closed by the interlocking ridges on the 

 upper and under lips, since there are present no muscles 

 adequate to the unclasping of these firmly united parts. 

 In that case the larva of this species feeds entirely by 

 means of the canals which conduct the juices of the 

 victim from hair-fringed openings on the tips of the 

 mandibles to the mouth cavity {Fig. i, /). The distal 

 portion of each canal seems to lie within the mandible 



May 20t/i, igi2. 



