2*8 



TREADWELL. 



ently karyokinetic, but in none of them is there the slightest re- 

 semblance to the normal cleavage pattern. 



Fig. 8 is of especial interest. In about twelve hours after 

 transfer from the salt solution to sea water, there will be found 



5 6 7 



FIG. 5. Trefoil stage. Preserved material. 

 FIGS. 6 and 7. Later development of stage shown in Fig. 4. Preserved material. 



numbers of swimming embryos, looking much like the half em- 

 bryo formed by destroying one blastomere of the two-cell stage. 

 It is apparently formed from an embryo like that of Fig. 4 by a 

 development of one cell, while the other remains undivided. 

 Since it seems probable that the latter is to be regarded as a cell 

 with an "extra ovate" attached, rather than a true two-celled 



FIG. 8. Embryo produced by development of half of embryo shown in Fig. 4. 

 Preserved material. 



FIG. 9. Embryo like that of Fig. 8. Living material. 



stage, we might say that here either the extra ovate or its fellow 

 developed, while the other part remained undivided. These di- 

 vided portions put out cilia, and swim about in the water, carry- 

 ing the undivided portion with them. Later, they break away 



