OF THE MOUTH PARTS OF CERTAIN INSECTS. 185 
Very interesting is the modification found in the Hmpzde, illustrating the extreme 
in the loss of parts; for here the hypopharynx is also wanting, though the salivary 
duct remains, opening into the grooved ligula, as shown in PI. III, Fig. 2%. In this 
case the hypopharynx is replaced by an extension and peculiar modification of the 
labrum. ‘This sclerite is elongated so as to extend to the tip of the labium, and is 
very much dilated, somewhat bulb-like at its base. In PI. III, Fig. 2%, labrum and 
ligula of Rhamphomyia longicauda are seen from the side, while in Pl. I], Fig. 13, are 
shown the same structures in Hmpis spectabilis. The edges of the labrum are turned 
under sufficiently to leave a central channel just large enough to receive the ligula, 
with which it then forms a closed tube through which the food is taken. 
In most of the Muscid flies we find a structure approximating Hristalis with the 
labial palpi removed; and the parts may be longer, or shorter, or differently developed, 
while adding nothing to what has been already shown; they are, essentially, reduced 
piercing structures, no longer functional. 
We have, however, in certain other species, where the mouth structures are short, 
very poorly developed labial structures. So in Hermetia mucens (P1. II, Fig. 14) the 
broad and large mentum bears only a short, scoop-like ligula. The specimen from 
which the figure was made was somewhat distorted in mounting and the ligula is 
turned just half round. Similar structures occur in the Bibionide, and Huparyphus 
bellus (Pl. J, Fig. 12) is not essentially different. 
Heretofore the hypopharynx has been referred to mainly in species in which it 
was feebly developed and played but a passive part as a covering structure. It is 
sometimes a highly specialized sensory structure, though it varies greatly, even when 
functional. 
A very curious type is found in Bittacus (Pl. ILI, Fig. 4’), where it takes the form 
of a simple cylindrical process, set with spines, almost like an odd joint of some slen- 
der palpus. In Copris carolina, Pl. I, Fig. 4, showing the epipharynx, may be 
accepted as a fair representation of the hypopharynx as well, save that the latter is on 
a much reduced scale. The opening of the salivary gland is in a dense mass of spe- 
cialized spinous processes. 
In the Libellula, among the dragon flies, we have an inflated, somewhat tongue- 
like organ (PI. I, Fig. 10”), in which the salivary duet is plainly traceable to its open- 
ing among a mass of crossed, specialized spines. The surface is richly supplied with 
sensory pittings and tactile hairs. It is a great modification from a structure of this 
kind to the simple, ribbon-like form of Bombus, or the flat, slender, chitinous form in 
Tabanus ; but the intermediate stages are all present. 
To recapitulate concerning the labial structures. The mentum and submentum 
Ne TE Se VOL SIDS Oe 
