DEVELOPMENT OF MOUTH PARTS 47 
adult insects of incomplete metamorphosis. There remains to determine the 
relations of the larval mouth parts of Simulium with its very different imaginal 
mouth parts. 
“In selecting flies for the study of the postembryonic development of the 
mouth parts I have chosen two which in the imaginal condition possess all the 
parts possessed by any fly, and these parts in as generalized condition as is to be 
found in the order, and which also possess in the larval stage a similarly full 
complement of mouth parts. Such larvee as those of the Muscide, with their 
problematical hooks and lack of other parts, and such imagines as the muscid 
flies, with no parts left except proboscis and maxillary palpi, are impossible for 
the determination of the relation between larval and imaginal parts. From the 
mouth parts of the imaginal Simulium and of other nematocerous forms it is 
Fic. 1.—Sagittal section through head of old larva of Simulium sp., showing 
forming imaginal head parts within. 
i.¢., larval head wall; i.d., imaginal derm; l@., larval antenna; i.a., imaginal 
antenna ; 7.¢., imaginal eye; i.md., larval mandible; peer eae mandible ; l.ma., 
larval maxilla ; i.ma., imaginal maxilla ; 1.1i., larval labium; 4. ,» imaginal labium, 
not difficult to trace the evolution to the specialized muscid conditions, and if 
the mouth parts of Simulium and similarly equipped flies can be interpreted, 
the various members of the dipterous series culminating in the muscids can. So 
in Simulium and Blepharocera I have found suitable forms for study ; both with 
females possessing the so-called mandibles, both with maxille and labium well 
developed in both sexes, and both with larve equipped with biting mouths with 
unmistakable mandibles, maxille, and.labia, and in one case, that of Simulium,. 
with the embryonic development of the larval mouth parts fully traced and the 
homologies certainly * determined. 
’“ Simulium sp.—tn the female imago ¢ the mouth parts consist of a short 
liplike labium composed of a short basal sclerite and three terminal lobes, being 
the two large paraglosse and a median short membranous lobe, the fused gloss ; 
a pair of maxille, each consisting of a basal sclerite, a long five-segmented 
palpus, and a single pointed, bladelike terminal lobe reaching nearly to the end 
* Metschnikov, E. Embryologische Studien an Insekten. Zeitschr. f. wiss. Zool., vol. xvi. 
1866; embryonic development of mouth parts of Simulium described on pe. 392-421. 
+ ‘In describing the adult mouth I shall assign to the various parts those names which, from 
my earlier study of the comparative anatomy, seem correctly used, and the use of which is 
confirmed by the results of this ontogenic study.” 
