l88 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



dantly provided with very supple bristles and also to the aspiration 

 occasioned by the dilatation of the cephalic stomodeal cavities and the 

 movements of the labiohypopharyngeal complex. It is not rare to 

 find in the lumen of the strongly dilated oesophagus several Chiro- 

 nomidae larvae, and even to be able to identify them. 



But apart from the mandible and maxilla described in detail by 

 Zavfel (loc. cit., pp. 582-585, figs. 12, 13), the characteristics of 

 w^hich have just been recalled, the differences between the orthocladian 

 (s.l.) and tanypin structures reside chiefly in the labroepipharynx 

 and the stomodeum and in the complex labiohypochilan. 



THE LABROEPIPHARYNX 



The labroepipharynx has only a few sensory setae, which are either 

 rods or vesicles with an innervated chaeta (cf. Zavi-el, loc. cit., pp. 

 579-582, figs. 7 to 11). No hooks, combs, other sclerites, or pre- 

 mandibles are present ; we find no trace in Macropelopia of all the 

 very abundantly differentiated labroepipharyngeal details of the or- 

 thocladian larvae. Only the labroepipharyngeal constrictor and tor- 

 mal muscles exist ; the latter has two-fiber groups, one having its 

 origin almost in the middle of the frontoclypeus, the other, stronger 

 and more lateral, being attached to the back of the head. The "pre- 

 mandibular vesicles" ("Praemandibularbliischen") of Zavfel are only 

 labroepipharyngeal expansions without muscular connections. The 

 clypeofrons is enlarged posteriorly. 



The cibarial atrium and the pharynx in its cephalic parts are en- 

 dowed with a powerful musculature, the radiated dilators of which 

 present a very characteristic X-shaped design on the cranium (cf. 

 Zavfel, loc. cit., figs. 3, 4). 



The whole of this musculature comprises the six following groups 

 (figs. 9 to 11): (i) the dilatores cibarii (MCib) with numerous 

 fiber groups, anterior to the frontal ganglion, here particularly de- 

 veloped ; the homologue in the orthocladian forms has only three or 

 four very slender fiber groups ; (2) the anterior dorsolateral dila- 

 tores pharyngis (Ph dla) ; (3) the posterior lateral dilatores pharyngis 

 (Ph dip) ; (4) the ventral dilatores pharyngis, posterior and lateral 

 {Ph vl) ; (5) the median dilatores pharyngis, posterior and dorsal, 

 with finer fiber groups the origins of which are disposed along the 

 sagittal line {Ph dm) ; (6) the pharyngeal circular muscles, antago- 

 nistic to the dilatores, against which the very slender internal stomo- 

 deal longitudinal fibers lean {M ann). 



