THE ANATOMY OF INSECTS. 15 



name applied by Kirby and Spence to it and to the other claw-like projections 

 of the maxilla. The French entomologists distinguish it as le premaxillaire. 

 Neither of these names is desirable ; the former is not restricted to this part of 

 the maxilla, but is often applied to the terminal portion of the lacinia; the latter 

 name is objectionable both in form and signification ; it is hardly appropriate 

 to apply the prefix prce to the most distal part of an appendage. I propose, 

 therefore, the name digitus for this sclerite. 



The Ldbium or Second Maxilla. The labium or under lip (12) is attached to 

 the cephalic border of the gula, and is the most ventral of the mouth parts. It 

 appears to be a single organ, although sometimes cleft at its distal extremity ; 

 it is, however, composed of a pair of appendages grown together on the middle 

 line of the body. In the Crustacea the parts corresponding to the labium of 

 insects consist of two distinct organs, very closely resembling the maxillae. In 

 this case they are termed the second maxillae, a name which is sometimes 

 applied to the labium of insects. Hence in defining the Hexapoda it is stated 

 that they have two pairs of maxillae. 



In naming the parts of the labium, entomologists 

 have usually taken some form of it in which the two 

 parts are completely grown together, that is, one 

 which is not cleft on the middle line (Fig. 29). 

 I will first describe such a labium, and later one 

 in whith the division into two parts is carried as 

 far as we find it in insects. 



The labium is usually described as consisting of 



. . FIG. 29. Labium of Harpalus. 



three principal parts and a pair of appendages. 1 he 



principal parts are the submentum, the mentum, and the ligula ; the appendages 



are the labial palpi. 



The basal part of the labium consists of two transverse sclerites ; the prox- 

 imal one, which is attached to the cephalic border of the gula, is the submen- 

 tum (a). This is often the most prominent part of the body of the labium. 



The Mentum (U) is the more distal of the two primary parts of the labium. 

 It is articulated to the cephalic border of the submentum, and is often so 

 slightly developed that it is concealed by the submentum.* 



The Ltgula (c) includes the remaining parts of the labium except the labial 

 palpi. It is a compound organ ; but in the higher insects the sutures between 

 the different sclerites of which it is composed are usually obsolete. Three 

 parts, however, are commonly distinguished (Fig. 29), a central part, often 

 greatly prolonged, the glossa (r 2 ), and two parts, usually small membranous 

 projections, one on each side of the base of the glossa, the paraglossce (c*}. 



* Unfortunately the term mentum is applied by some entomologists to the submen- 

 tum, and the true mentum entirely overlooked or distinguished by a different name. 

 This is the case in one of the most important works in the literature of American ento- 

 mology, "The Classification of the Coleoptera of North America," by Le Conte and 

 Horn. The student in the use of this indispensable work must bear this change of names 

 mind. These authors have termed the true mentum the hypoglottis, and state that in 

 Carabidae the homologous portion is often called the " basal membrane of the ligula" 

 (/. c. p. xviii). 



