1896.] Embryology. 765 
most careful scrutiny fails to detect the actual motion, or to see evi- 
dences of any movement of the protoplasm within the egg, which might 
cause the wrinkling. 
The furrow at the pole has become quite deep by the time its ends 
have reached the equator, in five or six minutes. The ends seem to stop 
here for a time, just at the border of the yolk area, while further changes 
take place in the pigmented portion. First the two edges of the groove 
approach each other at the pole, and seem to fuse slowly, the wrinkles 
entirely disappearing during the process. This fusion then extends in 
either direction along the groove for some distance, often half way to 
the equator, obliterating the wrinkles as it goes. By this means the 
groove may entirely disappear at the center while remaining near the 
periphery (Fig. 38). 7 
At this point the furrow begins to enter the yolk area on either side, 
and at the same time the groove reappears along the center of the pig- 
mented hemisphere. It now becomes very broad and deep. Indeed, it 
seems to reach clear through to the yolk, and its walls are considerably 
rounded on either side. But they are now smooth, so that the wrinkles 
remain in all fifteen or twenty minutes on the first furrow. 
This first furrow divides the egg into two nearly equal parts (Figs. 
3, 12, 28, 35). When its ends first reach the yolk area, where they 
stop for a time, as already noted, the two blastomeres thus formed are 
very much rounded at their ends, and diverge strongly from the groove. 
This is readily seen in the series given in figs. 1 to 4, but it becomes 
much more prominent after the reappearance of the groove—(Figs. 28 
to 30). Under a higher magnifying power a wide space can now be 
seen at either end between the two segments. The floor of this space is 
triangular in shape and doubly curved, being concave from side to 
side, and convex antero-posteriorly. It is formed of light colored yolk, 
into which the pigment shades gradually around the borders. The two 
segments are thus rounded in a manner very similar to that of the first 
two blastomeres of a meroblastic egg. 
As the furrow proceeds toward the inferior pole the space between 
the two pigmented segments diminishes, the borders of the furrow 
approach each other, and the surface of the egg becomes smooth once 
more, with the groove indicated merely by a narrow, faint line. 
It remains in this condition some eight or ten minutes before the 
second cleavage begins, and this may be called its resting stage. The 
rapid closing of the groove previous to the appearance of the second 
furrow occurs also in Amblystoma (Eycleshymer). 
