180 



AN ESSAY ON THE DEVELOPMENT 



paraglossse, and the three-jointed labial palpi. This generalized structure fixes tlie 

 relation of the parts, and from it we may pass to more specialized types. 



In Harjmlus cah'gmosus ( PI. Ill, 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 2)araglossa3. 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 cari-y our dissections one step ftirther and from the fresh specimen remove 

 not only the highly chitinized parts, but also the softer attached structures, leaving 

 maxillie and mandibles undisturbed, we find in all cases the ojsophagus in the cavity 

 below the mentum and submentum, and these sclerites afford attachments for neces- 

 sai'y muscles. They also form, by means of chitinous extensions and processes, a 

 chamber or cavity protecting the oesophagus and supplying muscular attachments 

 when a sucking or pumping sti'ucture is needed. Thus the mentum and submentum, 

 whether separated or united, are always inferior coverings to the oesophagus. 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 Andreiia vicina with jmrt of the epi- 

 pharynx still attached, and in /'olistes metricus, where the structures are complete. 

 Precisely the same structures occur in Simulium ( PI. I, Fig. 1''), as will be moi'e fully 

 noted hereafter. It may be stated that I have adoi)ted the term " fulcrum," used by 

 Macloskie and others, to designate the structure formed b}' the mentum and submen- 

 tum and containing the beginning of the alimentary canal. 



In Polistes metricus (PI. II, Fig. 18'') I show the labium completely dissected 

 out, with all its attaclnnents, viewed laterally. • It will be noted that here the mentum 

 and submentum are united, highly chitinized, and foi'm a scoop-shaped structure, 

 bearing at one end the labial structures and enclosing normally the beginning of the 

 oesophagus. 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. 11, Fig. 18", aie shown ligula 



