LIMITS OF DIVISIBILITY OF LIVING MATTER :5 % _!7 



vate and the egg. Four hours later this egg was in the 

 condition shown in Fig. 7l>. The cleavage cells lying within 

 the egg in Fig. IX have developed into the blastula c. The 

 niicromeres and the large cells inclosed between them in Fig. 

 To have developed into a misshapen mass of cells d in Fig. 

 7t>: each two of the four large cells of the extraovate have led 

 to the development of the separate blastulse <i and b, so that 

 we obtained from this one egg three blastulse and a mass of 



FIG. 77 



FIG. 78 



shapeless cells. 1 Fig. 77 shows the same egg twenty-four 

 hours later. The largest of the blastulse e, which has remained 

 within the egg-membrane, has developed into a gastrula, 

 while the two smaller blastulse a and 6, 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, 

 ami consequently go into "water rigor,'' do not all recover 

 and begin to segment at the same t line after they are returned 

 to normal sea-water. Under these conditions an extraovate 



i It often happened that the cells of the extraovate formed nt one, l>nt twor 

 iimri'. l)l;i-l 1 1 l:i'. Tin 1 .-liilinu' mot inn- nf t In- c.-IU arc nut rc-t ri<-ti-< I in I h<- I-M ra.>\ ati 1 , 

 it nil can t IrTcl'r , ri - 1,-a'l to \ ariuu-; t,'n>u|>int,'-i <>l" t hr 1-1 -11 -in a- -!<. ln>iili- of I In- !,"-'- 



membrane this origin of twins also occurs, but more rarely. Tin- tin 'ml i ram- n-stricts 

 tin- -li'lin^r motions of the cells. I -hall <li-ru-- tlii- qu<--tion in tfn-atrr drtail later 

 in a paper on the formation of double embryos. 



