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blastomeres of nearly equal size. Its progress over the blastodise is 
rapid, requiring but 5—8 min. to traverse the distance from the upper 
pole to the margin of the blastodisc. Beyond this margin it travels at 
a gradually decreasing rate until it reaches the vicinity of the equator 
where it either fades out or terminates abruptly. Its maximum 
extension appears to be reached at the time of the sixth or seventh 
cleavage. In no case have I observed the ends of this groove 
extending to the lower pole or even its vicinity. Neither have I ever 
found them terminating in or near the margin of the calotte. 
The second cleavage is also a meridional. It appears about 
30 min. after the first and is always foreshadowed by a rapid closing 
of the first cleavage groove. The two grooves of this cleavage usually 
begin at the same point and extend in opposite directions, giving rise 
to an apparently continuous groove as shown in Fig. 1. The grooves 
progress at the same rate as the first, passing from the center to the 
margin of the calotte in a few minutes, beyond the margin their 
progress is greatly retarded and not until several hours later do the 
grooves reach their maximum extension, finally terminating in a zone 
near the equator, sometimes slightly above the equator and again con 
siderably below. 
BALFOUR and PARKER figure these grooves as extending far below 
the equator, although not as reaching the lower pole. The description 
by Brarp leads to the conclusion that they actually reach the lower 
pole. Dran states that this cleavage “is expressed in the germ disk 
only and like the former furrow could not be traced in the yolk region 
of the egg”. 
Among all the eggs which I have examined I have never found 
one in which the grooves even extended as far as figured by BALFOUR 
and PARKER, and of course nothing approximating the description by 
BEARD. Neither have I observed anything like the condition described 
and illustrated by DEAN. 
The four grooves which constitute the third cleavage are in all 
cases observed vertical, usually occupying the relative positions shown 
in Fig. 2, conforming, in a general way, to the pattern of the 
Teleost. Their order of appearance is irregular, beginning in this or 
that quadrant. They pass over the surface of the egg at the same 
rate as those of the first and second cleavages, and finally terminate 
at about the same latitude. The pattern shown in Fig. 2 is very 
constant as found by both DEAN and myself, the variations from this 
type being few. , 
As to the character of this cleavage the authors again differ. 
