1020] Richmond, Studies on the Biology of the Aquatic Hydrophilidce 13 



the various structures. Dr. Bovin'g, who has studied the attachment of 

 muscles in larvae, has kindly offered valuable suggestions as to the homol- 

 ogies of the abdominal folds. 



The fully developed and typical hydrophilicl egg-case consists of 

 the egg-case proper, containing the eggs; a cap covering the entrance 

 to the latter and a projection continuous with the cap, which may be 

 either a horny mast, tube, or filament. In giving the measurements of 

 the case, the cap has always been considered as one end of the case. 



The head of the larva may be inclined, horizontal, or elevated, 

 with respect to the axis of the body, depending upon the shortening or 

 lengthening of its upper or lower side. The epicranial suture, which 

 may be present or absent, is formed by the union of the frontal sutures 

 along the median line. The gula is the sclerite to which the submentum 

 is attached. The epistoma is the sclerite just behind the clypeus and 

 its lateral expansions attain the front margin of the head just lateral 

 to the labro-clypeus. Schiodte called their angular projection the frontal 

 angle. The upper surface of the mouth region on the under side of the 

 labrum is the epipharynx; and. on the under surface, continuous with 

 the mentuin, is the hypopharynx. Ocular area is the term used for each 

 of the eye spots behind the antenna? because ocellus is misleading and 

 must be restricted to the adult. The antennal appendage is a finger- 

 like lobe borne by the second segment of the antenna, and there may be 

 two of these appendages. The lacina mobilis manclibuli is a flat unjointed 

 lobe which the posterior piece of the mandible bears; it is toothed 

 apically. The molar surface of the mandible is the grinding inner sur- 

 face near its base. The parts of the labium and maxillse may be seen in 

 Plate I, figs. 1 and 5. Palpifer is restricted to the palpus-bearing seg- 

 ment of the maxilla, while palpiger is applied to that segment of the 

 labium. "Articulating piece of maxilla" refers to the area between the 

 cardo and the labium upon which the maxilla articulates. 



A segment of the larva consists of a tergum, two pleura, and a 

 sternum. The folds of the abdomen are very confusing and need further 

 study. I have considered the hypothetical types of the abdominal 

 tergum as possessing four transverse areas, namely, the prsescutum, two 

 ^•ura and a scutellum. The preescutal area is flat, while the other areas 

 are represented by transverse folds. Between adjacent segments of the 

 abdomen, there is a prominent region which is called the " intersegmental 

 membrane." This may possibly be the postscutellum, but it has not 

 been considered as such in this paper. The number of folds in this area 

 is two at the most 



