Manchester Memoirs, Vol. hi. (1912}, No. II. 5 



portion of the canal leading from the mandible to the 

 mouth cavity projects strongly, and from his figure it 

 would seem very similar to the corresponding part in 

 Dytiscus Tiiarginalis {Fig. I, .v), hence I am inclined to 

 regard the process described by both these authors as a 

 palp-like projection of a still larger process, indicating, 

 perhaps, the occurrence of a more primitively constituted 

 maxillular rudiment in the larva of Cybister. 



The investigation of the mouth parts of various other 

 genera was not possible owing to lack of material, but it 

 is h6ped to extend the above limited observations during 

 the coming season, and also if circumstances permit to 

 inquire into the developments of these parts. Moreover, 

 certain features observed in the imago of Dytiscus mar- 

 ginalis suggest that the structure of the adult mouth 

 parts may throw some light upon the question of the 

 existence of maxillulae in the DytiscidcB.^ 



* In the cinrenl issue (vol. 57, part 4) of the Q. J. M. S. appeared a 

 carefully illustrated memoir, "The MoulhParts of Some Beetle Larvoe 

 (Dascillidi^ and Scarabreidix;), with especial reference to the Maxillulre and 

 Ilypopharynx," by Carpenter and MacDovvell, who point out the existence 

 of distinct maxillulie in the larvae of Helodes and Dascilhis. These authors 

 have also found it possible to detect corresponding structures, which are, 

 however, almost completely merged into the labium, in larvse of Geoirupes 

 and Phyllopertha. The existence of maxillula; in these Endopterygole 

 insects is a fact of great interest, and strengthens the idea of their occurrence 

 in the Dytiscidae. However, direct comparison between the maxillular 

 structures of these different types is not possible, owing to the highly 

 modified condition of the larval mouth-parts in Dytiscus and its allies. — ]. M. 



