38 DRAGONFLIES OF NORTH AMERICA 
segments is attained by the antennae in the 7th, and by the tarsi in 
the 8th instars: and that the lateral spines appear earlier on the 9th 
than on the 8th abdominal segment. During the first four instars the 
nymphs are practically colorless and very small, and after that the 
definitive characters of nymphal form are rapidly assumed. 
Walker has reported (’25, p. 28) the rearing of nymphs of Somato- 
chlora kennedyz through seven instars with somewhat similar results, 
as shown in the following table: 

Instars 1 2 3 4 5 6 Cf 
Length (ave.) ag 2:2 Qi 3-2 4.2 ? 1s 
Ant. joints 3 3 5 5 6 6 6 
Trs. joints 1 1 2 2 2 2 
Wings 0 0 0 r i i i 
Lat. abd. app. 0 0 0 r i i i 
Ment. setae 0 1 3 4 5 5-7 if 
Lat. setae 1 1 2 3 3-4 3-4 4 
These were from eggs laid in July that did not hatch until the follow- 
ing spring. These seven instars occupied an entire season, at the end 
of which the nymphs were less than one-third grown. 
The remarkable change that takes place at the end of nymphal life, 
making an aquatic creature over into an aerial one, is very well illus- 
trated by Dr. Kennedy’s figures of the black dragon, Hagenius brevisty- 
lus (fig. 19). After the final moulting every part of the body reappears 
in greatly altered form. It is, of course, prepared for in the last 
nymphal instar. The wings grow and become crumpled within their 
sheaths and flight muscles develop in the tense thorax. The genitalia 
also are developed and prepared for emergence; when freed from the 
narrow confines of the nymphal skin they quickly shape themselves 
after the pattern of the species. Figure 20 illustrates middle and end 
stages in the shaping process.* 
* The following is a memorandum made by the senior author at Havana, 
Ill., in 1896, of observations on the process of emergence in Gomphus notatus: 
“Boathouse, 5:30 p.m.; sun shining. Watched one emerge. It fastened its 
claws by swinging its entire body, rotating them, as if boring in; rested awhile; 
thorax appeared to be getting dry; nymph turned tip of abdomen forward; 
ejected water upon top of thorax (to soften it?) fifteen minutes after leaving 
water. Emergence began with a split of the skin which started between the 
wing pads and extended to head and across between eyes. Head freed first, 
mouthparts hanging limp; then legs and wings were withdrawn, together with 
entire thorax; body thus lifted at nearly right angles to the abdomen; held this 
