86 



CYTOKINESIS. 



of the daughter cells nearest the animal pole, fig. 100. While these movements are 

 taking place in the mesentoblast and its daughter cells, the substance of macro- 

 mere D rotates slightly to the right ; the nucleus and sphere lie deep in the yolk, by 

 which they are closely surrounded, text fig. XVI. In 4d and its derivatives the 

 spheres are not in contact with a free surface of the cell during the resting period, 

 and in these cells they become very indistinct and can only be clearly recognized 

 during the telophase. 



Fig. XXVI. 



Fig. XXVII. 

 Figs. XXVI-XXVII.— Two stages in the first division of the first quartette of Crepidula, showing the eccentric 

 position of the spindles and the approaching unequal division of the cells. 



(6). Sub-divisions of the First Quartette. — During and after the formation of 

 the first quartette, the rotations in these cells are dexiotropic. When the nuclei 

 have been carried from the left to the right side of each cell (figs. 90, 91), they are 

 then moved close into the inner angles of the cells (figs. 92, 93). Immediately 

 over the nuclei are the centrosomes and spheres ; the former are already spindle 

 shaped, figs. 91-93, and their long axes nearly coincide with the definitive spindle 

 axes. The central spindles then stretch over the upper sides of the nuclei, very 



