HUNGERFORD: AQUATIC HEMIPTERA. 233 



Fourth Iiistar. 



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 ai'cuate band of reddish-brown inter- 

 rupted on the median line. Two other pairs of smoky spots are upon the 

 disc 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 PecidiaHties. 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. 



Colo-r. Pattern as in fourth instar, only more striking and darker. 

 The two pairs of spots on disc of metathorax united to form a transverse 

 arcuate band. Posterior margin of metathorax with broad reddish-brown 

 band. 



Structural Peculiarities. Antenna 2-segment«d. 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 

 flo\\'ing 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. 0^'iposition 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. 



