516 H. H. Neu'r7jan 



ment. It is difficult to study whole embryos within the egg mem- 

 brane for a longer period, as they become too opaque and the 

 fluids within the membrane are apt to become cloudy and to 

 render outlines too vague to admit of camera drawings being 

 made. It was necessary for purposes of drawing and observation 

 to dissect out from the egg membranes both hybrid and pure 

 bred F. majalis embryos. 



If the specimens selected for drawing were active it was neces- 

 sary to quiet them with choloretone before drawings could be 

 made. It was frequently difficult to find a specimen that lay in 

 a position suitable for drawing and much patience was required 

 in order to find individuals that were at once typical and fortunately 

 disposed for drawing. 



For convenience in reference the four strains pictured in the 

 table (Plates II to IV) are lettered H, h, m, and M, capital letters 

 referring to pure strains and the corresponding small letters to the 

 hybrids from the same species of egg. (H) refers to pure bred F. 

 heteroclitus; (h) to the hybrid strain from the eggs of F. hetero- 

 clitus and the sperm of F. majalis; {m) to the hybrid from the eggs 

 of F. majalis and the sperm of F. heteroclitus; and (M) to pure 

 bred F. majalis. 



In the main body of the paper certain abbreviations will be 

 used without further explanation: 



For the pure F. heteroclitus strains the terms: pure heteroclitus, 

 H pure, or simply (H) will be used. 



For the hybrid strains from F. heteroclitus eggs and F. majalis 

 sperm, the terms: hybrid heteroclitus, H hybrid, or simply (A), 

 will be used. 



For the pure F. majalis strains the terms: pure majalis, M 

 pure, or simply (M), will be used. 



For the hybrid strains from the eggs of F. majalis and the sperm 

 of F. heteroclitus, the terms: hybrid majalis, M hybrid, or simply 

 (m), will be used. 



