58 CONKLIN. [Vol. XIII. 



each macromere, Diagram 8. These micromeres do not again 

 shift their position to any considerable extent until the general 

 rotation of the ectoblastic cap in the 52-cell stage. 



The fact that the micromeres are more firmly bound to each 

 other than to the macromeres is shown hereafter at almost 

 every stage ; it is first plainly indicated, however, in such 

 stages as Figs. 15 and 16, where the second quartette of 

 micromeres, in rotating in an anti-clockwise direction, carries 

 with it the first quartette, as if the whole formed a rigid plate 

 lying upon the macromeres. Evidence of this same fact is 

 farther shown by Fig. 16, in which the micromere 2b does 

 not lie in the furrow between A and B, though the other 

 micromeres of this quartette, 2a, 2d, and 2c, lie in the other 

 furrows. This is due to the fact that because of a very long 

 polar furrow between macromeres B and D, the first and second 

 cleavages are not at right angles to each other. Instead, 

 therefore, of shoving past la into the furrow between A and B, 

 the cell 2b remains in its proper position relative to the other 

 micromeres, although by so doing it cannot come into the 

 proper position relative to the macromeres. 



This fact that the micromeres are more loosely connected 

 with the macromeres than with each other may be in part 

 accounted for by the presence of a small rectangular segmenta- 

 tion cavity lying just over the polar furrow and under the first 

 set of micromeres. It is most clearly marked at the moment 

 when the first quartette is separated from the macromeres, and 

 it entirely disappears after the second quartette is formed. 



3. Division of the First Quartette of Micromeres and Formation 

 of the Turret Cells {Trochob lasts). Figs. 16, ly, Dia- 

 gram 4 {p. 60). 



Before the third and last quartette of micromeres is formed 

 the first quartette divides in a laeotropic direction, as shown 

 in Fig. 16. Division occurs at nearly the same time in each of 

 the cells, and the central moieties (lai-idi) remain considerably 

 larger than the peripheral ones (i^i^-id-). The smaller outer 

 portions do not again divide until very late in the cleavage, 



