154 CONKLIN. [Vol. XIII. 



of the protoplasm and nuclei is due to some force other than 

 gravity. 



In the process of overgrowth the smaller entoblasts, 4A, 4B, 

 and 4C/are carried around with the ectoblast and mesoblast to 

 the ventral side, and at the same time the whole egg is slightly 

 flattened from above downward, as shown by the enlarged 

 diameter of the egg when seen in polar view, Figs. 49-53, and 

 still better in the actual section shown in Fig. ^J. This change 

 of shape is partly due to the fact that these smaller entoblasts, 

 4A, 4B, and 4C, lie out on the periphery of the ^^'g and thereby 

 enlarge its horizontal diameter, and also to a certain flattening 

 of the macromeres themselves. The changes in the shape of 

 the gastrula are much greater after the next division of the 

 macromeres. 



2. The Fifth Quartette. 



The fourth quartette was separated from the macromeres by 

 laeotropic cleavage. The next division of these cells is more 

 nearly bilateral than spiral. Figs. 54, 57, 60, though it is typi- 

 cal of neither. I shall call the cells thus formed (5A-SD) the 

 fifth quartette, in conformity with the designations used for the 

 previous products of the macromeres, though the facts that 

 the division is not a spiral one and that the products are 

 purely entoblastic might, sensu stricto, make some other name 

 preferable. 



Rarely are more than two of the macromeres seen in division 

 at the same time ; in Fig. 54 A and C are dividing first, in 

 other preparations I have found B and C or A and B dividing 

 simultaneously. In D, however, the corresponding cleavage is 

 delayed until long after the division of A, B, and C, Fig. 59, 

 although it was the first cell to divide in the formation of the 

 fourth quartette. 



The division of A and B is very nearly bilateral with refer- 

 ence to the second or median cleavage furrow, and the new cells 

 formed, 5 A and 5B, lie on each side of that furrow and on the 

 ventral side of the macromeres A and B, Figs. 57, 58. 



The cleavage of C and D is less perfectly bilateral than that 

 of A and B, and the new cells, 5C and 5D, are cut off from 



^ Hereafter all entoblast cells are designated by capitals. 



