192 NORTH SHEA INVESTIGATIONS. 
as during the time I had the ovum under observation, a vesicle which 
appeared at first to be united by a narrow neck to the undifferentiated 
Fra. 1.—Unfertilized egg shortly after extrusion. 
region became entirely separated fromit. The process was probably 
taking place over the whole area, but it was only possible to observe 
the final constriction in the case of this particular segment, as none 
of the others were in profile. I conclude that the formation of the yolk 
seoments takes place after the hyaline enlargement of the ovarian 
ege has manifested itself, and, so far as my observations go, it 
appears to extend gradually from pole to pole. I am inclined to 
suspect that it may extend more rapidly along the periphery, since 
in examining some ova immediately after extrusion I failed to 
satisfy myself that the central region was segmented. Others, how- 
ever, at the same stage, and all older living ova examined, were 
segmented throughout. 
I attempted artificial fertilization, but do not think it was success- 
ful. Forty-eight hours later all the ova were dead, except a few 
kept in a vessel to which no milt had been applied. ‘These last 
presented the appearance shown in Fig, 2, <A very slight peri- 
vitelline space had appeared, and there was a small and slightly 
opaque blastodermic cap: the character of the yolk was unchanged, 
and the eggs still floated. 
The dead ova in all the vessels, whether supplied with milt or 
not, exhibited a similar blastoderm, which, as is well known, fre- 
quently appears without fertilization. The yolk presented a peculiar 
appearance, the segments being restricted to an irregular mass 
