46 THE AMPHIOXUS. 



remains however, as may be seen from Figures 3 

 and 4, attached to one of these pieces. 



The processes which have to do with the cell 

 nucleus next occupied my attention. In the but 

 slightly transparent living object it is to be noticed 

 that the cell nucleus apparently vanishes during the 

 process of division, and after this is completed is 

 again, visible as a clear spot in the centre of the seg- 

 mentation sphere. The same is to be observed in 

 the further divisions. 



FOUR-CELLED STAGE (Fias. 5-7). 



After a pause of about an hour the formation of 

 the second furrow begins. This is likewise a meri- 

 dional one, and is at right angles to the first. Both 

 segmentation spheres 1 are affected by this division at 

 exactly the same time. We have represented in 

 Fig. 5 the manner in which the furrow makes a 

 deeper cut on the outside, than on the contact surface 

 of the two cells. 



As a result of this segmentation we have four 

 spheres of equal size, on one of which the polar body 

 is still attached at the upper pole. The spheres are 



again flattened against each other, a proceeding which 



1 Blastomeres. 



