1916] Biology of Aquatic Lepidoptera 165 



Hatching.~ln- almost every case, the entire egg mass hatched 

 at about the same time. Occasionally, a few eggs lagged behind 

 but they hatched not later than five hours after the main group 

 of caterpillars had emerged. The first observed manifestations 

 o± the hatching process were motions of the larva within the 

 egg, consisting of a series of body contractions and expansions 

 combined with movements of the head. The mandibles were 

 also m active motion. Apparently, the combined action of the 

 mandibles and the body movements were responsible for the 

 breaking of the egg shell. In the egg masses under observation 

 the movements of the larv^ preliminary to hatching began 

 from four to six hours before the final escape. The larva 

 emerged from one end of the egg, escaped quickly, and assumed 

 an active habit. In egg masses deposited under natural condi- 

 tions, the number of imperfect eggs was very small not 

 exceeding three per cent. 



The dates of collection of egg masses varied from July 10 to 

 August 20. Possibly, differences of seasons have some influence 

 on the egg-laying period since in 1913 numerous egg masses, 

 •were found as late as August 20, while during the preceding 

 summer none were found later than July 30. 



The Larva (PI. VII, Figs. 1-3). 

 First Instar.—ThQ first instar has been briefly described bv 

 Forbes ('10, p. 221) as follows: " Stage I ( ) 



Slightly larger than N. gyralis? described below, with propor- 

 tionately much larger anal setas, without trace of gills. Head 

 nearly .3 mm.; length of large anal setae 1 mm." A careful 

 study of this instar has made it possible to extend the 

 description. 



The larva, in this instar (Fig. 1), is light yellowish brown in 

 general appearance. The body is elongate, subcylindrical and 

 tapers very slightly caudad. Body length of newly hatched 

 larv« varied from 1.26 to 1.5 mm. The maximum diameter is 

 m the region of the pro thorax where it is about 0.32 mm The 

 main divisions of the body and the intersegmental grooves are. 

 distinctly marked. Duration of first instar in specimens reared 

 m aquaria, about 7 days. 



Head approximately 0.3 mm. in width, smooth, shining, and 

 dark yellowish brown. Epicranial suture distinct. Front 

 clypeus and labrum light yellow. Labrum emarginate, setose' 



