246 WALTEE N. HESS 



work during the past year, a careful study was made of the 

 development of the light-organs in both the embryo and the 

 pupa. This has resulted in the modification of the tentative 

 views expressed in the preliminary report. 



The author is indebted, especially, to Dr. William A. Riley, 

 under whose supervision the greater part of this study was 

 made, also to Dr. O. A. Johannsen for his helpful suggestions and 

 criticisms. 



MATERIALS AND METHODS 



Eggs were obtained, for a study of the embryonic develop- 

 ment of the light-organs, by confining ripe females in jars that 

 had been partly filled with earth and moss. Since oviposition 

 occurred very readily in captivity, it was easy to obtain a com- 

 plete series of eggs by removing the insects to different jars 

 each day. 



The different larval and pupal stages were obtained by col- 

 lecting second-year larvae in April and confining them in jars 

 with earth and moss. By observing them each day, desired 

 stages could be selected. 



Two complete sets of eggs_, late larvae, and pupae were ob- 

 tained as described above. The eggs were collected at intervals 

 of twenty-four hours, from the time of oviposition until hatching. 

 The pupae were collected at twenty-four-hour intervals from the 

 time of pupation until emergence. Several stages of late larvae 

 were obtained previous to pupation. One set of this material 

 for histological purposes was fixed by heating in water at a 

 temperature of 80°C. for four minutes, after which it was trans- 

 ferred to alcohol. These eggs were punctured with a fine needle 

 immediately after heating, in order to insure good preservation. 

 The chorion of each egg was later dissected off to expose the 

 embryos. The other set of material was fixed in Flemming's 

 fluid (strong formula). These eggs were punctured and allowed 

 to remain for twelve hours in the fixer, after which the chorions 

 were removed and the eggs were returned to the fixer for another 

 twelve hours. The first twelve hours of fixation was sufficient 

 to harden the embryos so that their chorions could be dissected 

 off, while the last twelve hours insured, good fixation. In the 



