OF TIIK MOUTH PARTS OF CERTAIN INSECTS. 185 



Yavy interesting is the modification found in the Emindoi, IWnstvatmg the extreme 

 in the loss of parts ; for here the hypopharynx is also Avanting, though the salivary 

 duct remains, opening into the grooved ligula, as shown in PI. Ill, Fig. 2". In this 

 ease the hyi)opharynx is i-eplaced by an extension and peculiar modification of the 

 labrum. This sclerite is elongated so as to extend to the tip of the labium, and is 

 very much dilated, somewhat bulb-like at its base. In PI. Ill, Fig. 2", labrum and 

 ligula of Ultamjjhomi/ia longicavdn are seen from the side, while in PL II, Fig. 13, are 

 shown the same structures in Emjns sjiedahilU. The edges of the labrum are tuined 

 under sufficiently to leave a central chaimel just large enough to receive the ligula. 

 with which it then forms a closed tul>e through which the food is taken. 



In most of tlie Muscid flies we find a structure api)roximating Enstalis with the 

 labial i)alpi removed; and the parts may l)e longer, or shorter, or differently develoj)ed, 

 while adding nothing to what has been already shown ; they are, essentially, reduced 

 piercing structures, no longer functional. 



AVe have, howevei", in certain other species, where the mouth structures arc short, 

 \ei-y poorly developed labial structures. So in Ilermctia mucens (PI. Ill, Fig. 14) the 

 l)road and large mentum bears only a short, scoop-like ligula. The specimen fi'om 

 which the figure was made Avas somewhat distorted in mounting and the ligula is 

 turned just half round. Similar structures occur in the Bibvm/da', and Euparyj)lms 

 hellus (PI. I, Fig. 12) is not essentially different. 



Heretofore the hypopharynx has been referred to mainly in species in which it 

 was feebly developed anil played but a i)assive part as a covering structure. It is 

 sometimes a highly specialized sensory structure, though it varies greatly, even when 

 functional. 



A very curious type is found in JiiWicus (1*1. 11 1, Fig. 4'), where it takes the form 

 of a simple cylindrical process, set with spines, almost like an odd joint of some slen- 

 der palpus. In Coj)7-is Carolina, PI, I, Fig. 4, showing the epipharynx, may be 

 accepted as a fair representation of the hyp<)i)hai'yn.\ as wt'll, save tiiat the latter is on 

 a nnich reduced scale. 'Vhc o^icning iif the salivary ghind is in a dense mass of spe- 

 cialized spinous processes. 



In the Lihcllida, among the dragon flies, we have an inflated, somewhat tongue- 

 like organ (1*1. I, Fig. 10 ). in wliich the salivary duct is plainly traceable to its open- 

 ing among a mass of crossed, specialized spines. The surface is richly supplied with 

 sensory pittings and tactile hairs. It is a great modification from a structure of this 

 kind to the simple, ribbon-like Ibrm of liumhus, or the flat, slender, chitinous form in 

 Tahanus ; but the intermediate stages are all present. 



To reca])itulate concerning liie labial structures. The mentum and snbmentum 



