Limits oF DivisiBILITy oF Living MATTER 327 
vate and the egg. Four hours later this egg was in the 
condition shown in Fig. 76. The cleavage cells lying within 
the egg in Fig. 73 have developed into the blastula c. The 
micromeres and the large cells inclosed between them in Fig. 
75 have developed into a misshapen mass of cells d in Fig. 
76; each two of the four large cells of the extraovate have led 
to the development of the separate blastule a and b, so that 
we obtained from this one egg three blastule and a mass of 
FIG. 77 FIG. 78 
shapeless cells.' Fig. 77 shows the same egg twenty-four 
hours later. The largest of the blastulze c, which has remained 
within the egg-membrane, has developed into a gastrula, 
while the two smaller blastule a and b, which have remained 
outside the egg, have developed no further. A short time 
after this drawing was made all four pieces began to swim 
about in the drop. The formation of the blastula therefore 
occurred at the same rate in the smaller masses as in the 
larger one. I may add that it also occurred at the same rate 
as in the eggs whose membrane had not burst. One notices, 
of course, that eggs which are placed into dilute sea-water, 
and consequently go into “water rigor,” do not all recover 
and begin to segment at the same time after they are returned 
to normal sea-water. Under these conditions an extraovate 
1It often happened that the cells of the extraovate formed not one, but two or 
more, blastula. The sliding motions of the cells are not restricted in the extraovate, 
and can therefore lead to various groupings of the cell-masses. Inside of the egg- 
membrane this origin of twins also occurs, but more rarely, The membrane restricts 
the sliding motions of the cells. I shall discuss this question in greater detail later 
in a paper on the formation of double embryos. 
Digitized by Microsoft® 
