700 THE AMERICAN NATURALIST. [VoL. XXXVI. 
For a complete developmental study of the mouth parts of 
any dipteron it would be necessary to begin with the budding 
appendages of the head segments in early embryonic life, to 
trace the development of these appendages to their definitive 
form in the hatched larva, and finally to follow the transforma- 
tion, if it occurs, of these larval parts into the ultimate imaginal 
ones. Asa matter of fact, such actual transformation does not 
occur, so that the study of the postembryonic development of 
the mouth parts con- 
sists of noting the ec- 
dysis of the larval parts 
y and determining the 
ontogenic relations of 
the new imaginal parts 
to the old larval ones. 
As for the embry- 
onic development of the 
mouth parts, —7.e., the 
development from bud- 
ding appendages to 
definitive larval parts, - 
— that has been done 
for several Diptera, 
and in particular by 
Metschnikov for Simu- 

+h d. 1 rem d 
Fic. 1g. — T bryonic stages i p 
imulium sp. (after Metschnikov): younger stage at 
left, older at right; in upper row whole embryos from lium ; One of the two 
lateral aspect, in f l f heads of 


flies whose postembry- 
onic development I 
shall describe. These embryonic studies make certain the 
homologies of the larval parts; in those flies like Simulium, 
whose larvæ are provided with a biting mouth with full com- 
plement of parts, it is easy to note plainly the development of 
mandibles, maxillæ, and labium from the successive pairs 
of budding head appendages (Fig. 19), and thus to homologize 
these parts certainly with the mandibles, maxillæ, and labium 
of adult insects of incomplete metamorphosis. There remains 
to determine the relations of the larval mouth parts of Simu- 
lium with its very different imaginal mouth parts. 
stages. £4., ephalic lobes » anf. , antenna ; snd., 
mandible; mr., illa; Zi, labium. 
