612 EMBRYONIC DEVELOPMENT OF GASTEROPODS. 



Embryonic Development of Boris bilamellata : — a, Ovum, con- 

 sisting of Enveloping membrane a and yolk b ; b, c, d, e, f, suc- 

 cessive stages of Segmentation of Yolk ; G, first marking-out of 

 tbe sbape of tbe Embryo ; h, Embryo on the 8th day; i, the same 

 on the 9th day; k, the same on the 12th day, seen on the left 



