STUDIES OF FERTILIZATION 369 
3. The entrance cone then gradually retracts, drawing the 
membrane down to form a depression in which the spermatozoon 
is included. At this stage one may easily imagine that the sper- 
Fig. B. History of the fertilization-cone as seen in the living egg. Four cam- 
era drawings of the same egg :— 
a Seventeen minutes after insemination, 
b Nineteen minutes after insemination, 
c Twenty-two minutes after insemination, 
d Twenty-four minutes after insemination, 
The fertilization-cone is shown at the height of its development in a, its gradual 
recession and the simultaneous formation of a depression in the membrane is 
shown in b, ¢ and d. 
. 
matozoon has been taken into the egg, as it is apt to be concealed 
in the depression of the membrane; but this is not the case. The 
stage of best development of the depression, corresponding to 
