248 BULLETIN OF THE 
At 9h. 10m. a.m. (PIL I. fig. 8) the primary furrow, pr., has deepened 
still more, and the constriction has encroached more than before on the 
whole circumference, so that now the two hemispheres of the egg are 
connected by a narrow band or “bridge” of protoplasm, ‘the breadth 
of which is about .05mm. The longer diameter of the egg is .35 mm. ; 
the shorter, .25 mm. 
At 9h. 20m. a. m. (PI. I. fig. 9) the constriction has grown wholly 
around the egg and the primary furrow has deepened so much that a 
small protoplasmic band .02 mm. in diameter is all that now connects 
the two cells. The other dimensions are about the same as the corre- 
sponding diameters of the egg at 9h. 15m. a. M. (fig. 9), although it 
was noticed that one hemisphere of the 2-cell stage was slightly 
smaller than the other. 
At 9h. 25m. a. m. (PL I. fig. 11) the cell which was the smaller has 
grown in size so that now both cells of the 2-cell egg are of uniform 
size. At 9h. 30m. a.m. (fig. 12) the two cells have been pressed 
closely together, and the first plane of cleavage (1 cl. pl.) has been 
fully formed, although the undivided part of the egg still remains in 
the form of a slight bridge connecting the two cells which form the egg. 
No nuclei were observed in either of the cells. 
It will thus be seen that the development of the 2-celled ovum from 
the time the primary furrow first appears up to that when the first 
cleavage plane is well formed is forty-five minutes. For a long time 
after the formation of the first cleavage plane has been effected, both 
hemispheres of the egg exhibit abnormal changes by which the egg 
is made to assume curious, often grotesque forms. Here and there over 
the surface of the egg rise pseudopodic elevations, which sometimes take 
the form of long rhizopodal threads. Later, these extensions sink back 
into the substance of the egg and new combinations arise. The two 
spheres, or hemispheres, now draw away from each other, or become 
squeezed together. They lose their globular, symmetrical form, and 
their profiles become more angular, or sometimes the angles are pushed 
out into conical projections. These changes often foretell the immediate 
death of the egg, but full as often take place in healthy ova which reach 
a good old age. 
A considerable length of time may elapse before the initial changes 
leading to the formation of the second plane of cleavage can be detected. 
We are not in my judgment justified in supposing that the vital forces 
of the egg are “resting” at that time until we know more accurately 
the state of the interior and the changes which are going on there. 
