142 
Psyche 
[December 
long, maximum width 1.0 mm. Lateral gills similarly 
flattened, triquetral ; left lateral gill 2.1 mm. long. Tillyard 2 , 
when speculating upon the evolution of the horizontal 
lamellar type of gill in his Australian Argiolestes, postu- 
lated just such an intermediate form as this between the 
primitive saccoid gills and the specialized lamellar types. 
It seems reasonable to assume that this nymph represents 
one of the intergrade types leading to the specialized situa- 
tion in the Australian species. The gills are attached to 
the abdomen by a remarkably narrow constriction, a very 
efficient breaking point. In cross-section can be seen the 
vertical internal laminae which are characteristic of the 
horizontal gill type (PI. 14, fig. 2). The hypodermis and 
tracheae are heavily pigmented. The tracheae enter the 
gill as a single trunk, divide immediately into the two 
main trunks which then divide repeatedly throughout the 
length of the gill. Long slender setae densely cover the 
gill. They are held in unusually deep, cup-like sockets 
which keep the processes in an erect position. 
It would be interesting to study the life-history of this 
species in view of the apparent shift in habit, and to 
compare it with closely related aquatic forms. When the 
nymph was received, it was heavily coated with debris 
caught among the long hairs. In this immature form, 
respiration must take place through the cuticle. The in- 
creased number of setae serves to maintain a cover of 
damp debris which keeps the cuticle moist, a necessity 
for gas exchange. Such a cover is also of advantage as 
protective coloration. Lieftinck (in litt.) feels that the 
hairiness of this nymph may be, however, a common 
2 1917. On the morphology of the caudal gills of the larva of Zygopterid 
dragonflies. Proc. Linn. Soc. N. S. W., 42: 31-112, 606-632. 
Explanation of Plate 14 
Megapodagrionid nymph, Ciu, New Caledonia. Fig. 1, outline diagram 
of cross-section through caudal gills to show relative shapes and positions. 
Fig. 2, reconstruction of cross-section through middle of left lateral gill. 
Fig. 3, right mesothoracic leg. Fig. 4, ventral view of left lateral gill, 
dbc, dorsal blood channel; dn, dorsal longitudinal nerve; il, vertical in- 
ternal lamina; tr, tracheal trunk. 
Magnification. Fig. 3 (xlO). Figs. 1, 4 (x20). Fig. 2 (x67). 
