OP THE MOUTH PABTS OF CERTAIN IXSECTS. 181 



and paiaglossK of this same I'olistes. The structures arc here membranous, some- 

 what bladder-like, and well adapted for lapping by means of flattened, bent processes, 

 set in series on the entire inner sni'face. The paraglossio are completely separated and 

 the mouth opening is shown at the base of the figure, as well as the chitinons I'ing 

 marking the beginning of the (esophagus. 



In Andrena vicina (PI. I, Fig. 9) we find a similar yet quite ditlerent structure, 

 i. e., the same jjarts, used for much the same purpose, yet considerably modified in de- 

 tail. The mentum is here much longer, more shallow, but similarly bears the epiphar- 

 yn.\ on chitinous rods. The ligula is more infiated and the paraglossie are nuich 

 reduced, but the palpi originate as before, and we have simply an illustration of the 

 variation in form found in th.is united mentum and submentum. It is important to 

 note here that in /'olistes, Andreaa, and indeed the Hymenoptera generally, the lal)ial 

 structures are free from all lateral attachments to the head and may sometimes be pro- 

 jected forward quite a distance. The attachment to the head, indeed, is muscular and 

 membranous entirely, and there is no direct articulation to any point by chitinous or 

 rigid processes. There is nothing therefore to prevent the growth of the head sclerites 

 around the mentum, which would thus become an internal structure — as has actually 

 happened in the Diptera. 



Another feature upon which Dr. Packard rightly places great stress is that a 

 salivary duct opens into the hypopharynx at the base of the ligula, which he thereby 

 identifies. As this ligula is always attached to the mentum, it follows that this struc- 

 ture may be identified in the same way, while no sti'uctures not originating from the 

 same point can be labial in character. 



Before studying further the specializations of the labial structures, it may be well 

 to say that they sometimes tend to become useless or obsolete, or so much i-educed that 

 they are difficult of recognition ; and, curiously enough, in such eases the palpi seem 

 to be the persistent organs. Thus in some species of Scoliidce among the Hymenop- 

 tera the mentum bears only little, feebly developed palpi. A striking case is in the 

 Panorpidio, where on PI. Ill, Fig. 4'', the mouth structui'cs of Jiittacus sirigosu-^ are 

 shown. Here ligula and paragloss;e have disappeared entirely ; but the palpi are dis- 

 tinct and the curiously developed hypophai'ynx mai'ks the beginning of the opening 

 into the oesophagus. 



A modification of this type is to be found in the Lepidoptera, where practically in 

 all cases the palpi alone, attached to a plate of variable size and shape, represent the 

 labial structures. 



It seems a long jump from the reduced type in I'anorpidxe to the fully developed 

 labium of the Ajmhi' ; yet, except for the fact that all the parts are nuicli elongated, 



