PLATE XXI. 



Fig. 1. Two eggs of Notonecta undulata after hatching, showing the 

 characteristic slit in the shell and the clear embryonic membrance shed 

 by the nymph upon emerging. 



Fig. 2. Adult Notonecta undulata in the water. 



Fig. 3. Egg nearly ready to hatch. Note the red eye spot and the 

 dark line at margin of the gelatinous substance which glues the egg to 

 its support. 



Fig. 4. A freshly laid egg viewed from above. 



Fig. 5. A roadside pool in early spring. The back-swimmers were 

 arriving in numbers, flying from some unknown quarters where they 

 had passed the winter. 



Fig. 6. Eggs of Notonecta undulata, freshly laid upon old weed stems 

 lodged in the waters of the pool. Gyrinid beetles lay somewhat similar 

 eggs, which may be distinguished by their arrangement upon their sup- 

 port and by the fact that the eye spots in advanced eggs are black 

 instead of red, and farther from the end of the egg than in those of the 

 back-swimmers. Plate first used in Ento. News, XXVIII. 



(308) 



