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 shovi^ sooty black. The micropylar plate darkens. The 

 micropylar tube remains w^hite. 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 mai'ked 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, pi. 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. itisulata. 

 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 nj'mphs have no ventral abdominal median carina. 



