180 AN ESSAY ON THE DEVELOPMENT 
paraglosse, and the three-jointed labial palpi.. This generalized structure fixes the 
relation of the parts, and from it we may pass to more specialized types. 
In Harpalus caliginosus (P1. III, Fig. 7) we have a case where the ligula forms 
a single, central organ, laterally bounded and on one side completely enveloped by the 
softer paraglossze. The location of the palpi remains essentially the same. We have 
here two cases showing the change of a two-jointed membranous paired organ into a 
single, rigid, chitinous structure, and the identity of the parts is not questioned, nor 
I believe, questionable. 
If we carry our dissections one step further and from the fresh specimen remove 
not only the highly chitinized parts, but also the softer attached structures, leaving 
maxillze and mandibles undisturbed, we find in all cases the cesophagus in the cavity 
below the mentum and submentum, and these sclerites afford attachments for neces- 
sary muscles. They also form, by means of chitinous extensions and processes, a 
chamber or cavity protecting the cesophagus and supplying muscular attachments 
when a sucking or pumping structure is needed. Thus the mentum and submentum, 
whether separated or united, are always inferior coverings to the cesophagus. To sup- 
port this structure, processes sometimes extend almost or quite to the upper or anterior 
surface of the head, and in many cases, where the epipharynx is separated from the 
labium, it is connected by means of long processes with the mentum. This is true in 
many Coleoptera, quite usual in the Hymenoptera, and occasionally found also in the 
Diptera. In PI. I, Fig. 6, is a lateral view of the labium of Copris carolina when 
completely dissected out, and the clubbed processes, loosely attached to the inferior 
prolongation of the submentum, normally support the epipharynx. In PI. I, Fig. 9, 
and Pl. II, Fig. 18, we note similar processes in Andrena vicina with part of the epi- 
pharynx still attached, and in Polistes metricus, where the structures are complete. 
Precisely the same structures occur in Simuliwm (P1. I, Fig. 1“), as will be more fully 
noted hereafter. It may be stated that I have adopted the term “ fulcrum,” used by 
Macloskie and others, to designate the structure formed by the mentum and submen- 
tum and containing the beginning of the alimentary canal. 
In Polistes metricus (P\. I, Fig. 18’) I show the labium completely dissected 
out, with all its attachments, viewed laterally. It will be noted that here the mentum 
and submentum are united, highly chitinized, and form a scoop-shaped structure, 
bearing at one end the labial structures and enclosing normally the beginning of the 
cesophagus. Attached by long chitinous rods to the posterior angles is the epiphar- 
ynx, so that hypopharynx and epipharynx are borne on the same base, are closely op- 
posed to each other and may be manipulated by muscles arising close together. The 
origin of the palpi is shown from the mentum. On PI. II, Fig. 18%, are shown ligula 
