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 'O2 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 



FIG. 96. Three ova from a mature egg-tube, c, outer cellular layer of the chorion ; 

 ch, epithelial chorion of a young egg ; ch.,, inner layer of the chorion of mature 

 e gg 5 n -2> an d o ;t , eggs in different stages of development ; o 3 , 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. 



