
No. 429.] THE MOUTH PARTS OF INSECTS. 685 
There is no special difficulty, outside of the general difficul- 
ties which the study of insect embryology commonly presents, 
in tracing from beginning up to completed larval condition the 
development of the mouth parts of insects with complete meta- 
morphosis; and the homologies of these larval mouth parts 
with the mouth parts of adult insects with incomplete metamor- 
phosis can accordingly be determined on a basis of ontogenic 
study (also, of course, on a basis of comparative anatomy). 
The biting mouth parts of the more generalized flies, of the 
lepidopterous caterpillars and coleopterous grubs, can be 
homologized with the mandibles, maxilla, and labium of the 
adult cockroaches and locusts, constituting the generalized 
biting or so-called orthopterous mouth. But when the attempt 
is made to carry the homologies on to the adult piercing and 
sucking mouths of the flies and butterflies we lose in the pre- 
pupal stage our grip on the continuity of embryonic and adult 
mouth conditions and find ourselves forced to rest our interpre- 
tation of the homologies of the adult dipterous, lepidopterous, 
and hymenopterous mouth on the basis of comparative anatom- 
ical studies. And fortunately for us the persistence of certain 
generalized forms already referred to enables us to make a 
pretty secure determination of these homologies for all of the 
orders except the Diptera. To my mind, indeed, the study of 
the comparative anatomy of the mouth parts of the generalized 
flies (families of the Nematocera) enables us to be pretty cer- 
tain even in that order, but such an attempt! of mine in 1899 
has certainly failed to be convincing to several entomologists. 
There is necessary, then, the completion of the tracing of 
the development of the mouth parts; nothing less, under the 
circumstances that the most generalized of dipterous mouths 
are not at all generalized (if one may be so paradoxical), but 
are so specialized that no safe determination of the homologies 
can be made on the basis of comparative anatomy, — nothing 
less will be convincing or satisfactory for the solid grounding 
of an interpretation of the homologies of the mouth parts of 
1 The Mouth Parts of the Nematocerous Diptera, Psyche, vol. viii (1899) : I, 
PP- 303-306, January; II, pp. 327-330, March; III, pp. 346-348, April; IV, 
PP- 355-359, May ; V, pp. 363-365, June; with 11 figs. 
