DRAGONFLIES AND DAMSELFLIES IN PONDFISH CULTURE. 199 
MOUTH PARTS OF ODONATE IMAGOS. 
DRAGONFLY ImMacos.—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 setee and very much shortened. From its anterior margin projects the median 
lobe, greatly enlarged in Anax and Aischna (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 Atschna they are enlarged into concave lamelle, 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 
Bee ea ere iors mtn, emesis zy ™™ line, both hooks have practically 
entirely disappeared, and the 
lobes are covered with hairs. The mandibles (figs. 31 and 34) and the maxille (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, curved, and sharply pointed, and the 
molars (m) near the base, which are much shorter and armed with separate cusps or 
points. The maxille still retain the outer lobe or palp (p), which is curved and covered 
with hairs, and the inner lobe, which is armed with curved and sharply pointed teeth 
and a pad covered with long sensory hairs. 
DaAMSELFLY ImMaGos.—In the damselflies the general structure of the mouth parts 
is the same as in the dragon flies. Here the median lobe of the labium (ml, fig. 35) is 
fully as long as the lateral lobes, is divided by a deep median fissure, and is covered with 
long hairs. The lateral lobes retain the immovable end hook (e), which is very long and 
slender and curved to an acuminate point, and the movable hook (mo), which is also long 
and narrow, but is bluntly rounded and covered with hairs. These lobes are relatively 
much narrower than those of the dragonflies, and, when folded, only the terminal hooks 
meet on the median line. The mandibles (fig. 36) and maxille (fig. 37) are similar in all 
respects to those of the dragonflies, except that there is a sharper distinction between the 
incisors and the molar in the mandibles, while the maxillz have long hairs on the outer 
margin near the base. 
The gizzard in the imago is relatively much smaller and weaker in the nymph, and 
has very little functional use. The chitin ridges or folds along its walls are still retained, 
