. Bulletin of the Bureau of Fisheries. Fisheries; Fish culture. DRAGONFLIES AND DAMSELFLIES IN PONDFISH CULTURE. MOUTH PARTS OF ODONATE IMAGOS. 199. Dragonfly Imagos.—When the nymph transforms into an imago, the hinged mask disappears, and the labium or lower lip is now attached directly to the ventral surface of the head. In consequence there is a much greater similarity in the mouth parts of the im- agos, though there are still some differences. In general, the labium of the imago consists of a basal portion, corresponding to the mentum of the nymphal mask, but destitute of raptorial setae a
. Bulletin of the Bureau of Fisheries. Fisheries; Fish culture. DRAGONFLIES AND DAMSELFLIES IN PONDFISH CULTURE. MOUTH PARTS OF ODONATE IMAGOS. 199. Dragonfly Imagos.—When the nymph transforms into an imago, the hinged mask disappears, and the labium or lower lip is now attached directly to the ventral surface of the head. In consequence there is a much greater similarity in the mouth parts of the im- agos, though there are still some differences. In general, the labium of the imago consists of a basal portion, corresponding to the mentum of the nymphal mask, but destitute of raptorial setae and very much shortened. From its anterior margin projects the median lobe, greatly enlarged in Anax and ^schna (fig. 29) and covered with hairs, but reduced to a small triangular piece in the Libellulids (fig. 32) and more or less free from hairs. On either side of the mentum is a side piece known as the squame (ms) which sup- ports the lateral lobe. These latter now fold together across the front of the face in all the imagos. In Anax and ^schna they are enlarged into concave lamellae, strongly convex on their outer borders and covered with hairs. The inner border ends distally in a sharp end hook (e) which is immovable; just outside of this is a larger movable hook (mo), which is rounded and palplike and covered with hairs. When the lobes are folded across the front of the face, these four hooks meet on the median line, but the margins of the lobes beyond them diverge rapidly. In Erythemis (fig. 32) and the other Libellulids the margins of the lateral lobes, when folded, meet each other in a long median Hne, both hooks have practically entirely disappeared, and the lobes are covered with hairs. The mandibles (figs. 31 and 34) and the maxillae (figs. 30 and 33) have changed a little in detail, but are practically the same as before. The teeth of the mandibles are very strong and may be divided into two sets, the incisors (in) at the tip of the mandible, which are long, curve
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectfisheries, bookyear19
