ON THE STRUCTURE OF THE EGG IN THE BLOW-FLY. 679 
also developed with its dorsum towards the dorsal aspect of the 
egg, and its cephalic extremity at the anterior end. 
The Chorion, or egg-shell, is opaque, with a pearly-white 
lustre. Its whole surface is divided into beautiful regular 
hexagonal fields, having a long diameter of 04 mm. and a short 
diameter of oz mm. The surface of each field exhibits a fine 
punctation. After the deposition of the eggs, the chorion, 
which is at first tough and leathery, becomes so brittle that it 
Fic. 96.—Three ova froma mature egg-tube. ¢, outer cellular layer of the chorion ; 
ch, epithelial chorion of a young egg ; c/y, inner layer of the chorion of mature 
CGE} 4, %, and oy eggs in different stages of development; 0,, a portion of a 
mature egg showing the infolding of the chorion at the micropyle; yy, yelk 
cells and yelk. 
can be readily removed with a pair of needles and a little 
practice from the subjacent vitelline membrane. This enables 
the student to observe the developing embryo in optical section 
through the transparent vitelline membrane. I have found it 
useful to make a sketch in this way of hardened embryos 
before embedding them for sections. The whole process is of 
course performed in the fluid in which the eggs are preserved. 
I prefer Flemming’s mixture. 
