HUNGERFORD: AQUATIC HEMIPTERA. 233 
Fourth Instar. 
Size. Length of body, 2.86 mm.; width of body, 1.38 mm.; width of 
head, 1.2 mm.; distance between eyes, 0.494 mm. 
Color. Pattern distinct. Head with median dark longitudinal band. 
Wing-pads dark, covered with dark pile. Caudal margin of meso- 
thorax smoky. Metathorax with an arcuate band of reddish-brown inter- 
rupted on the median line. Two other pairs of smoky spots are upon the 
dise of the metathorax. A pair of small triangular spots separated by a 
narrow median line of pale and a larger pair of indefinite quadrangular 
smoky blotches laterad of these. The intersegmental lines of abdomen 
reddish-brown, very distinct. The large dark abdominal scent glands 
open by paired pores on caudal margin of the fourth and fifth seg- 
ments. The abdomen is marked by a smoky submarginal band and each 
segment bears two pairs of rectangular smoky gray spots, the outer ones 
forming distinct longitudinal rows. 
Structural Peculiarities. Wing-pads reach to the posterior margin of 
the metathorax, as in other Corixids. 
Fifth Instar. 
Size. Length of body, 4.21 mm.; width of body, 1.61 mm.; width of 
head, 1.46 mm.; distance between eyes, 0.624 mm. 
Color. Pattern as in fourth instar, only more striking and darker. 
The two pairs of spots on dise of metathorax united to form a transverse 
arcuate band. Posterior margin of metathorax with broad reddish-brown 
band. 
Structural Peculiarities. Antenne 2-segmented. Wing-pads extended 
past the posterior margin of thorax, as in other Corixids of the same 
instar. 
Summary. Arctocorixa alternata has the widest range of waters of 
any of the boatmen studied. It has been the only one commonly taken in 
flowing streams. The species winters as an adult and begins mating in 
the region of Ithaca, N. Y., about the middle of April, while the waters 
are still very cold. Copulation takes place under water and lasts some- 
times for hours. Oviposition begins shortly and continues until some of 
the young become adult, if not longer than this. The eggs hatch in from 
one to two weeks, depending on the temperature, and the instars require 
about one week for each stage. The last stage occupying a few days 
longer. The first generation emerges about the middle of June. 
—— 
