. Bulletin of the Bureau of Fisheries. Fisheries; Fish culture. 194 BULLETIN OF THE BUREAU OP FISHERIES. Mask.—The most noticeable thing about a nymph is the so-called mask, which is folded back beneath the head and which may or may not cover the lower part of the face (fig. 6), This mask is really the lower lip or labium, whose outer end terminates in three lobes, one median and two lateral; the latter may take the form of stout claws (^schnidae) or of spoon-shaped lamellae (Libellulidae). The mask is hinged near the center and when not in use is folded at the hinge; the lateral lobes are tur
. Bulletin of the Bureau of Fisheries. Fisheries; Fish culture. 194 BULLETIN OF THE BUREAU OP FISHERIES. Mask.—The most noticeable thing about a nymph is the so-called mask, which is folded back beneath the head and which may or may not cover the lower part of the face (fig. 6), This mask is really the lower lip or labium, whose outer end terminates in three lobes, one median and two lateral; the latter may take the form of stout claws (^schnidae) or of spoon-shaped lamellae (Libellulidae). The mask is hinged near the center and when not in use is folded at the hinge; the lateral lobes are turned inward across the front end of the median lobe, and the whole apparatus is folded back beneath the head. Figure 7 is a side view of the head of L. Itictuosa, showing the mask folded back, while the lateral lobes at its tip cover the lower half of the face. This is the con- dition found in the nymphs of all the Libellulidae. Figure 9 is a side view of the head of Anax Junius; here the lateral lobes do not cover the face at all, but extend straight forward as stout claws beneath the chin. This condition is found in the nymphs of the .^schnidae, with the exception of the genus Cordulegaster, and as an accompanying character the head is depressed or flattened. The length of the labium varies considerably in different dragonflies, but is usually longer in the .^schnidae than in the Libellulidae and reaches back, when folded, between the bases of the second legs. With the mask folded the nymph either conceals itself in the mud or trash on the bottom or steals up on its prey and when within striking distance shoots the mask forward in front of the head and grasps the victim between the lateral lobes. Figures 8 and 10 show the same two specimens of luctuosa and Junius with the mask thus extended. The distance which they can reach, of course, varies with the size of the nymph and the length of the mask; some of the large Anax nymphs can cover 15 to 25 mm. This, in addition to the
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectfisheries, bookyear19
