550 The American Naturalist. [June, 
amined, the variation in mouth-part characters is considerable. 
In all, the characteristic large labrum (see figs. 1 and 2, lb., 
plate XXV), overlying the basal part, at least, of the haustel- 
lum (h) was present. The rudiments of mandibles were ob- 
served in but one species, Hallesus sp. The maxille present 
either rudiments of a free lobe, as in Mystacides punctatus (see 
fig. 2, ma. 1, plate XXV), or the lobe in a well-developed, sense- 
hair covered, probably functional condition, as in Hallesus sp, 
Setodes sp, Hydropsyche scalaris, and others. The basal part of 
the maxilla is sometimes pretty plainly divisible into cardo 
and stipes, as in Hydropsyche scalaris ; more often, however, not. 
The labium usually presents a conspicuous, characteristic, ex- 
panded, and longitudinally striated flap, the haustellum (see 
fig. 1 and 2, h., plate XXV), composed by the fusion of the 
terminal labial lobes. In Hydropsyche scalaris I was interested 
to discover the labium not so modified. The outer lobes were 
free and of rather large size; the inner lobes were represented 
by a pair of short, blunt tubercles, free from any indication of 
fusion with each other or with the outer lobes, the rudiments 
of free lobes. 
In general the mouth-parts of the Trichoptera, where func- 
tional, may be held to exhibit the following characteristics ;, 
the absence of mandibles (or, at best, the presence of rudimen- 
tary functionless ones), maxille with basal portion often dis- 
playing distinguishable cardo and stipes, with functional lobes 
or distinct rudiments of both or of one free lobe, prominent 
several-segmented maxillary palpi, labium with its lobes free 
or coalesced to form the characteristic haustellum or lapping 
organ, labial palpi 3-segmented, prominent, (see figs. 1 and 2, 
plate XXV). Conspicuous and characteristic also is the large, 
flap-like labrum, which overlies the base of the haustellum, 
and aids materially in the half-lapping, half-sucking mode of 
taking food, which Lucas attributes to the Trichoptera. This 
conspicuous labrum is strikingly paralleled by the exception- 
ally large and well-developed labrum of Micropteryz, a feature 
not referred to in the previous discussion of the mouth-parts 
of this genus. In all the species of Micropteryz examined by 
me the labrum is large, appearing as a prominent triangular 
