OF THE MOUTH PARTS OF CERTAIN INSECTs. al 77 
get at the steps by which the present “beak” was developed, and my material is not 
sufficient for that purpose. The mandibulate type, on the contrary, proved well 
adapted for variation, and its differences and modifications are here traced. 
For convenience, Kolbe’s figures of the mouth parts of a grasshopper are repro- 
duced on Pl. III, Fig. 22, and may be referred to in connection with the following 
explanation. 
In a well-developed mandibulate mouth we have, forming an upper lip, the lab- 
rum, often notched in front or toothed; but never a paired organ, never with appen- 
dages, and never mechanical in function. It is articulated at base to the clypeus and 
serves to shield or protect the mouth in front; as a matter of fact, not a functional 
mouth structure at all. It is marked ldr in all figures. 
More or less intimately associated with it on the inner side is the epipharynx, which 
is compared in function with the palate of vertebrates, and is furnished with sensory 
hairs, pegs or pittings. It may be so closely united with the labrum as to form, prac- 
tically, a part of it, or may be entirely free. If free from the labrum, the epiphary nx 
is more closely united with the other mouth parts, and in such cases its supports go to 
the mentum or labial structures. Not infrequently it has attachments to both. In 
form it may be a mere pointed process, or it may be a more or less divided, plate-like 
organ; but its functions are gustatory or sensory in all cases—it never becomes a 
functional mechanical structure, and I have never found it without a more or less de- 
veloped labrum to shield it. It is lettered ep? in all figures. 
Just below these covering and gustatory organs is a pair of mechanical structures 
—the mandibles—set, one on each side of the head, and attached to the inferior margin 
of the epicranium or an extension from it. These mandibles are never jointed, rarely 
bear appendages, and never such as are functional, rarely have a movable tooth, and 
are usually solid and highly chitinized. They are actually made up of a number of 
sclerites, laterally united, but distinguishable in certain types like Copris, Pl. I, Fig. 8. 
I have elsewhere named and homologized these sclerites; but as the matter is not in 
dispute, and of no importance here, a simple reference to the figure in which they are 
named is all that is necessary. The position of this pair of mouth structures is inva- 
riable. They are completely disassociated from the maxillary or labial structures and 
remain attached to the head when all the other parts are removed in a body. They 
attach by socket joints to the epicranium and their tendons and muscles attach to 
its inner surface. They never change in function, never become united with or 
attached to the other mouth organs and never become internal structures. When not 
needed for chewing or biting the tendency is to obsolescence: never toward a change 
into a thrusting or piercing organ, so far as my observations extend. 
A. P. S.—VOL. XIX. W. 
