Experimental Studies on Germinal Localization. 227 



these bore a tuft of short, weak ciHa, by means of which the 

 larva very slowly rotated. In view of the structure of the Ys- 

 macromere larva, it is probable that this ciliated cell (or cells) 

 represents at least a part of the posterior group of cilia which I 

 have assumed to contribute to the ventral ciliated tract in the nor- 

 mal larva. 



Fig. VIII. 



(Figs. 75-81 X 250; Fig. 82 X 300). 



Isolated 1/16 Basal, and Isolated Cell of Second Quartet, Patella. 



75, first division of 1/16 basal; "jG, second division (64/16), 4 formed; 77, 

 product, 24 hours; 78-81, cleavage of isolated 2; 82, product, 24 hours, with two 

 trochoblasts and pre-anal (?) cells. 



3. Isolated blastomeres of the second quartet ( i/i6-embryo) . 



These blastomeres, obtained by successive isolations, divide like 

 the foregoing as if still forming part of a complete embryo. The 

 first division is nearly or quite equal. In the second division one 

 of the cells divides nearly equally, the other very unequally. Thus 

 arises a 64/16-stage (Figs. 78-81) that is closely similar to the 



