No. 429.] THE MOUTH PARTS OF INSECTS. 7901 
In selecting flies for the study of the postembryonic devel- 
opment of the mouth parts I have chosen two which in the 
me 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 
larvae as those of the Muscidz, 
with their problematical hooks and 
lack of other parts, and such imag- 
pow 20. — Mouth aed * adult — i à à 
, female. Zep. ines as the muscid flies, with no 
th bona Km. nae ar parts left except proboscis and 
mk palpus; Z., labium; Az, para- maxillary palpi, are impossible for 
3 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 
not difficult to trace the evolution to the specialized muscid 
conditions, and if the mouth 
parts of Simulium and similarly 
equipped flies can be inter- 
preted, 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 pos- 
sessing the so-called mandibles, 
both with maxille and labium 
well developed in both sexes, 
and both with larvae equipped 
with biting mouths with unmis- 
takable mandibles, maxillae, and s- . md, mandible; sa, mas mel 
: s : maxillary lobe; #x.f., maxillary palpus ; 
labia, and in one case, that of z., labrum; eA, epipharynx; Zi, labium; 
Simulium, with the embryonic %4» bypopharax. 
development of the larval mouth parts fully traced and the 
homologies certainly! determined. 
1 Metschnikov, E Nut logische Studien an Insekten, Zeifschr. J wiss. Zool, 
P eo 





