HUNGERFORD: AQUATIC HEMIPTERA. 187 
Color. White when first deposited, then amber as the red eye spots 
begin to develop. The ventral surface of the embryo (upper surface of 
egg) begins to show sooty black. The micropylar plate darkens. The 
micropylar tube remains white. Later the darkening embryo within 
lends a color pattern to the outside. 
Structural peculiarities. Shell rough, tough, irregularly, hexagonally 
reticulate. The egg increases in size as embryo develops within. 
First Instar. 
Size. Length, 2 to 2.6 mm.; width of body, .99 mm.; width of head, .91 
mm.; width between the eyes at front of head, .494 mm.; distance between 
the eyes, .364 mm. 
Color. Much darker than any other backswimmer nymphs examined. 
In ventral view, the legs, beak, hairs and venter, sooty black. Eyes dark 
red. Hind tarsi marked transversely by a broad band of lighter color 
and the margins of first three or four abdominal segments lighter also. 
Frons lighter than beak. In dorsal view, the head is light between the 
eyes. Thorax and abdomen dark save where the light band of the head 
extends backward on the thorax to the abdomen. Margin of basal seg- 
ments of abdomen somewhat lighter. (See drawing, pl. XIX, fig. 2.) 
Structural peculiarities. Besides its much darker color, which readily 
separates it from the other nymphs, the posterior margin of the middle 
femur is equipped with only one well-defined, spiniferous tubercle. 
The first instar nymphs of the four species reared may be distinguished 
as follows:* 
A. Color dark, smoky testaceous. Posterior margin of middle femur 
with one long spine on a tubercle. N. irrorata. 
AA. Color light. Posterior margin of middle femur with 2 spines on 
tubercles. 
B. Length, 2.6 mm. or more. Posterior margin of hind femur 
with 10 to 11 stout spines, plus 2 longer ones at distal end. 
N. insulata. 
BB. Length, less than 2.6 mm. Posterior margin of hind femur 
with 7 or 8 short spines, plus 2 longer ones at distal end. 
C. Legs conspicuously banded. Spines on posterior margin 
of hind femur not conspicuous. Margin of abdomen nar- 
row, rather slender body: N. variabilis. 
CC. Legs not conspicuously banded. Spines on posterior mar- 
gin of hind femur conspicuous. Margin of abdomen 
wide, robust nymphs. N. undulata. 
Second Instar. 
Size. Length, 3.27 mm.; width of body, 1.5 mm.; width of head, 1.2 mm. 
Color. For color pattern see later instars. 
Structural peculiarities. The median abdominal carina is now present 
on the venter and margined with hairs. Posterior margin of mesothorax 
more arcuate than in first instar. The distance between the eyes at ver- 
* First instar Notonecta nymphs have no ventral abdominal median carina. 
