4 



INTRODUCTION. 



this organ is very much developed ; indeed the latter family has 

 been styled from this fact Palpicornia by some authors. Under- 

 neath the maxillae and forming the floor of the mouth is found 

 the mentum, which, together with the ligula (a variable process 

 situated in front of the mentum), makes up the labium or lower 

 lip ; the term ligula, however, is sometimes loosely applied to 

 the front portion only of the ligula proper, which is in some 

 genera considerably extended, and apparently, but not really, 

 distinct. From supports situated at the base of the ligula arise 

 the labial palpi, which in general style, as a rule, resemble the 



Fig 



3. — Labium of Calosoma sycophant a. 

 m., mentum ; d., tooth of mentum ; 

 epl., epilobe of mentum ; squ.p., 

 squama palpigera ; 1, 2, 3, joints of 

 labial palpi ; lig., ligula ; par., 

 paraglossa ; g., gula ; s.g., gular 

 sutures. (After Ganglbauer.) 



Fig. 2.— Maxilla of Calosoma syco- 

 phanta. c.,'Cardo; st., stipes; 

 squ.p., squama palpigera; Li , 

 internal lobe of maxilla ; I.e., 

 external lobe of maxilla, two- 

 jointed ; 1, 2, 3,4, joints of 

 maxillary palpus. (After Gangl- 

 bauer.) 



maxillary palpi; these are usually 3-jointed, sometimes 2- join ted and 

 rarely setiform. On each side of the front of the labium is often 

 found a more or less developed membranous appendage, known as 

 the paraglossa : these are sometimes connate, or almost connate, 

 with the labium, but often extend, as curved points or blunt 

 projections, considerably beyond its apex. 



The eyes are very variable in size and shape ; they may be round, 

 oblong, kidney-shaped, deeply emarginate or entirely divided, as 

 in Gyrinus. In this latter genus and its allies the beetle is provided 

 with four distinct eyes, two on the upper surface of the head and 

 two on the under surface, so that it is admirably adapted for its 

 usual position on the surface of the water. The number of facets 

 in the eyes is also very variable, though not so much so, perhaps, 



