OF THE MOUTH PARTS OF CERTAIN INSECTS. 193 
incomplete articulation between galea and subgalea. By separating off the galear 
structures, the relation of palpifer and lacinia in Simuliwm is illustrated (on PI. I, 
Fig. 1°), and the convergence of the two at tip is not distortion, though perhaps a 
little exaggerated by pressure. The result of this change of position is that a section 
made near the base of the proboscis would show as illustrated on Pl. I, Fig. 2’, while 
one made nearer the tip would show as in Fig. 1°. Incidentally it will prove interest- 
ing to compare these sections with that of Bittacus strigosus (Pl. III, Fig. 4"), leaving 
out of consideration the abnormal labium of the latter. The resemblance is perfect, 
and the resemblance expresses fully the actual condition of the matter. A very simi- 
lar state of affairs exists in the Astlidw (Pl. IU, Fig. 1°). Here the palpifer is the 
only maxillary piercing organ, and the figure itself shows clearly how easily it would 
swing inside the ample space left in the subgalea for its entrance. The curvature of 
the organ is such, also, that when in place it meets the central ligula so as to form a 
solid puncturing organ. 
So in Chrysops (Pl. II, Fig. 14) the structure is seen to be similar to that in 
Simulium ; but here, as almost everywhere else in the order, it is cylindrical or nearly 
so, in marked contrast with the lacinia, which is always flattened. 
As we get into types that have lost the piercing habit, the function of the palpifer 
fails or changes. If the species have a short, nonflexed proboscis, it simply dwindles 
from disuse. So in Stratiomyia and in Leptis (Pl. II, Figs. 1 and 2) it simply forms 
a little chitinous appendage to the palpus—a mere remnant without function. If, on 
the other hand, the species are able to flex the proboscis, another change takes place. 
There is needed then some lever to which muscles for flexing can be attached, and no 
structure seems to have been so easily adaptable as the palpifer. So we find in the 
Eimpide, where only slight flexion is required, only a small basal extension, shown at 
Pl. I, Figs. 4 and 3, for Hmpis spectabilis and Hulonchus tristis, and at Pl. IIT, Fig. 
2’, for Rhamphomyta longicauda. 
In the Bombyliide is a step forward. The insects are not predaceous, have the 
habit of hovering over flowers and using the proboscis in feeding in that position. 
This requires a much better control, and as a result the basal extension is much better 
developed, as shown in Pl. II, Figs. 6 and 7, illustrating Bombylius and Anthraa. 
As we get into types like Hristalis and other Syrphide, the basal extension be- 
comes the most prominent and the piercing portion diminishes in size (Pl. H, Fig. 5), 
and keeping step with this modification is a gradual separation of the palpus itself 
from the palpifer. This is well illustrated both in Hristalis and Spherophoria, and 
this tendency continues until in Duerllia (Pl. II, Fig. 10) the separation is complete, 
though the piercing portion of the palpifer is yet distinguishable. In Callephora even 
A. P. S—VOL, XIX. Y. 
