hungerford: aquatic hemiptera. 191 



Hatching and Behavior of Newly Hatched. Hatching takes place upon 

 bursting the cephalic end of the egg as shown in the photograph. The 

 nymph comes forth swathed in a clear membrane, gradually working its 

 way, by backward and forward movements, till it is nearly clear of 

 the egg shell, whereupon the embryonic sheath splits and slowly the new 

 bug frees itself, the swimming legs being the last to leave the shell. 

 As the legs are freed they spring out into position. When at last the 

 little bug is clear, it rests as though exhausted, then it makes, during 

 the next fifteen or twenty minutes, intermittent endeavors to attain the 

 surface. In these efforts it approaches the surface head uppermost and 

 is heavier than the water — dropping to the bottom as soon as its 

 struggles cease. Finally it may succeed in hooking a front claw into 

 the surface film where it will hang suspended for some minutes. Finally 

 it turns on its side, pierces the surface film, then darts below, the guard 

 hairs closed over a bubble of air. Up to this time the guard hairs of 

 the abdomen have rested limp against the body. 



Number of Instars. There are five nymphal instars. 



Food Habits. The food habits of the first three instars are very in- 

 teresting to watch. The Uttle nymphs make a specialty of Ostracods and 

 other little Entomostracans. They will devour each other and thus each 

 little nymph must be isolated if he is to grow up. 



Behavior. This species, more than any other, rests at the surface 

 film. Christine Essenberg has written much concerning four species of 

 Backswimmers. 



DESCRIPTION OF STAGES. 

 The Egg. 

 Size. Length, 1.625 mm. to 1.813 mm.; diameter, .5 mm. to .6 mm. 

 Shape. Elongate oval; becomes plumper as embryo develops within. 

 Color. White when first deposited. The embryo lies with its back 

 to the attached side of the egg as a rule. After a few days incubation 

 the eye spots begin to appear as faint pink blotches, darkening as de- 

 velopment takes place, till shortly before hatching the black hairs bor- 

 dering the various portions of the body of the nymph are visible through 

 the chorion. The surface of the egg is tough and rough, due to the fact 

 that it is sculptured in irregular hexagons. The micropyle is a curved 

 tube arising from a circular differentiated area as shown in the drawings 

 on plate XX. 



First Instar. 



Size. See table below. 



Color. General body white, eyes red, hairs and spines black, antenna 

 smoky black. When first hatched the abdomen especially transparent 

 and the movements of the organs plainly visible within. Tarsal claws 

 all conspicuously black. 



Structural Peculiarities. The most characteristic feature of the 

 first instar is the absence of the tuft of hairs which in all succeeding in- 

 stars is found on a median ventral carina of the abdomen. The eyes are 

 relatively far apart. The antennae are apparently 2-segmented and di- 



