416 FRANK R. LILLIE 
top of the egg, and the equator of the egg. Fig. 1 6 shows the 
amount of jelly formed about three minutes after insemination; 
the cortical layer is already much reduced. Fig. 1 ¢ was taken 
twelve minutes after insemination; it shows a great increase in 
amount of jelly due not only to continued secretion from the egg, 
but also, presumably, to swelling of the jelly already formed. The 
walls of the alveoli which contained the jelly-forming spherules 
may be seen on the right side of this photograph crossing the peri- 
vitelline space to the plasma membrane. On the upper side may 
be seen the fertilization cone and external to it outside the vitel- 
line membrane the spermatozoon. A conical pointer of ink is 
directed to the spermatozo6n. This forms regularly in eggs in- 
seminated in ink and is due to the ink particles pressing in along 
the tail of the spermatozo6n embedded in the jelly, owing to their 
Brownian movements. This ink cone remains even after the 
spermatozoon has penetrated and thus serves as indicator of the 
point of entrance of the spermatozo6n up to the time of cleavage. 
A study of the relation of the point of entrance to the first cleavage 
plane by one of my students is now under way (see Just, ’12). 
Text fig. 2 is a drawing from the living egg based on such a pho- 
tograph as 1 c. The details are all clearly shown here and are 
described in the legend of the figure. 
b. The fertilization cone. The spermatozoon, that remains 
after the first jelly-formation, is attached by its perforatorium to 
the vitelline membrane. The protoplasm of the ovum immedi- 
ately beneath now forms a conical elevation (fertilization cone) 
which crosses the perivitelline space and becomes attached to the 
vitelline membrane beneath the spermatozo6n (text figs. 1 ¢ 
and 2). The fertilization cone then gradually retracts and dis- 
appears, drawing the vitelline membrane with it so as to form a 
depression in which the spermatozo6n is included. At this stage 
one may easily imagine that the spermatozo6n has been taken into 
the egg, as it is apt to be concealed in the depression of the mem- 
brane; but this is not the case. The stage of greatest develop- 
ment of the depression, corresponding to the complete retraction 
of the fertilization cone, is about twenty-two to twenty-five min- 
utes after insemination (see figs., Lillie 711, p. 369). 
