702 THE AMERICAN NATURALIST.  [Vow. XXXVI. 
Simulium sp. (Figs. 20-23). — In the female imago! the 
mouth parts (Fig. 20) consist of a short liplike labium (Z.) com- 
posed of a short basal sclerite and three terminal lobes, being 
the two large paraglossze (fg.) and a median short membranous 
lobe, the fused glossz ; of a pair of maxillae (»x.), each consist- 
ing of a basal sclerite, a long five-segmented palpus (mx.p.), and 
a single pointed, bladelike terminal lobe (;zx./.) reaching nearly 
to the end of the third palpar segment, serrate on its inner 
margin at the tip and better developed than in most Nema- 
tocera; and of a pair of short mandibles (md.), broad, thin, and 
weakly chitinized. As in other nematocerous flies, there is a 
well-developed labrum-epipharynx (/ef.) and an elongate flat- 
tened hypopharynx (/yp.). In the males the mandibles are 
wanting. | 
In the larva (Fig. 21) the mouth is of the biting type, with 
short-toothed and heavy mandibles (md.), short, jawlike maxilla 
(mx.) with distinct one-segmented palpus (sx. .), and a small, 
strongly chitinized labium (Z.) or labial plate. In addition, 
labrum (/é.), epipharynx (z7.), and hypopharynx (/yf.) are all well 
developed. 
The head of the larva having a thoroughly opaque, strongly 
chitinized cuticle, it was impossible to clear whole heads suffi- 
ciently to make visible the developing imaginal head and its 
parts, so that the method of sections had to be relied on to 
reveal the internal conditions. These sections of heads of 
larvae of various ages show plainly that the general method of 
development of the imaginal parts within the larval head, and 
the correspondence between forming imaginal parts and the 
corresponding larval parts already noted in the other orders of 
holometabolous insects, hold good in the Diptera. Fig. 2? 
shows in sagittal longitudinal section the forming imaginal 
head parts within the larval head. This section shows partic- 
ularly well the relation of the forming imaginal antenna to the 
vol. xvi, 1866 ; embryonic development of mouth parts of Simulium described on 
PP. 392-421. 
In the adult mouth I shall assign to the various parts those names 
which, from my earlier study of the comparative anatomy, seem correctly used, 
the use of which is confirmed by the results of this ontogenetic study. 

Li 
