196 



BUI^LETIN OI? THE BUREAU OF FISHERIES. 



armed with stout, curv^ed claws, while the inner is covered with stiff hairs ; these maxillae 

 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. Bach ridge carries projecting teeth, whose number 

 and arrangement varies a little in different species. The general character of these 



Fig. 15.— Maxilla of Anax Junius nymph. FiG. i6.— Maxilla of Erythemis simplicicollis nymph. FiG. 17.— i-Iandible of Anax 

 Junius nymph. Fig. 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 Nymphs. — The structure of the mouth of the damselfiy nymph is in 

 all respects similar to that of the dragonfly. The mask (fig. 25) is more like that of the 

 Tibellulidae, with raptorial setae 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 

 maxillse (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 

 1 6 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 small 

 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)- 



