196 BULLETIN OF THE BUREAU OF FISHERIES. 
armed with stout, curved claws, while the inner is covered with stiff hairs; these maxille 
are evidently used to help hold their prey securely (figs. 15 and 16). 
Mandibles.—The second pair are the mandibles; they are much stouter, are hard 
and chitinous, and are armed with strong teeth (figs. 17 and 18). They can easily 
crush the shells of small pond snails like Limnea, Physa, and Planorbis, or they can 
bite through the hard chitin covering of beetles and water boatmen. ‘The food con- 
tents of the stomachs of all the nymphs examined shows that the mandibles are used 
chiefly for crushing the food and not for chewing it. It is chewed only enough to get it 
down the gullet, and much of it is swallowed whole. 
Gizzard teeth—The real mastication takes place in the gizzard, and for this purpose 
the wall of the gizzard at the posterior end is armed with four longitudinal ridges of 
chitin—two dorsal and two ventral. Each ridge carries projecting teeth, whose number 
and arrangement varies a little in different species. The general character of these 
Ac. 15.—Maxilla of Anax junius nymph. Fic. 16.—Maxilla of Erythemis simplicicollis nymph. iG. 17.—Mandible of Anaz 
juniusnymph. Fic. 18.—Mandible of Erythemis simplicicollis nymph. 
toothed ridges is well shown in figures 19 to 24. The churning of the gizzard grinds the 
food against the teeth and soon reduces it to finer fragments; it then passes on into the 
intestine. 
DAMSELFLY Nympus.—The structure of the mouth of the damselfly nymph is in 
all respects similar to that of the dragonfly. The mask (fig. 25) is more like that of the 
Libellulide, with raptorial sete on the lateral lobes and the mentum, but the lateral 
lobes only cover a very small portion of the lower face. The mandibles (fig. 26) and the 
maxille (fig. 27) are so much like the larger ones of the dragonflies that they can be 
recognized at once by comparison. In the gizzard we find a somewhat different arrange- 
ment; instead of 4 chitin ridges there is some multiple of 4 up to as many as 32, 8 and 
16 being the most common numbers. Each ridge has a row of small spinelike teeth along 
the anterior half of both lateral margins; there is a narrow space through the center 
which is unarmed, and the whole posterior surface is covered with short stout spines, 
curved forward (fig. 28). Such a mill ought to be able to grind the food into very smail 
fragments, and we find that this is actually done. In other damselflies the gizzard varies 
greatly both in the number of ridges and in the size and number of the teeth. The differ- 
ences in the various genera and species have been admirably worked out and figured by 
Miss Higgins (1901). 
