248 BULLETIN OF THE 



At 9 h. 10 m. A. M. (PI. I. fig. 8) the primary fiuTow, pr., has deepened 

 still more, and the coiistrictiou 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 .05 mm. The longer diameter of the egg is .35 mm. ; 

 the shorter, .25 mm. 



At 9 h. 20 m. a. m. (PI. I. fig. 9) the constriction has grown wholly 

 around the Qg^, 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 9 h. 15 m. a. m. (fig. 9), although it 

 was noticed that one hemisphere of the 2-cell stage was slightly 

 smaller than the other. 



At 9h. 25 m. a. m. (PI. 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 d. pi.) has been 

 fully formed, although the undivided j^art 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 foi'mation 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 Qgg, 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. 



