2l6 



Edmund B. Wilson. 



43^ 



Fig. IV. 



Isolated Primary and Secondary Trochoblasts. 



(Figs. 34-39 X 250; Figs. 40-48 x 290). 



34, primary trochoblast (1/16, i-), obtained by successive isolation; 35, 36, 

 result of first division; 37-39, various forms after second division; 40, product 

 of Figs. 34, 36, 37, after 24 hours; 41, 42, similar individuals of the same age 

 and history; 43, pair of primary trochoblasts, 24 hours, the products of i^-i or 

 i2.2 (1/32); 44, 45, single primary trochoblasts. 24 hours, products of i^-i-i, 

 i2-^-2, etc. (1/64); 46, pair of secondary trochoblasts, 24 hours, the products of 

 1^-2; 47, 48, single secondary trochoblasts, 24 hours. 



less intermittent, sometimes ceasing wholly and again suddenly 

 being resumed. Sudden mechanical shock frequently causes a 

 sudden suspension of activity, followed immediately by a more 

 vigorous activity than before. Careful study of these embryos, 

 especially when they are dying, shows that the cilia in each cell 

 beat in the same direction; but owing to the fact that the rows 



