Plate VI. 



Entire Eggs of C. plana ; four to forty -five cells. 



(The figures of this plate are oriented as in the preceding one, the first cleavage furrow running from 

 top to bottom, the second from left to right ; the left lower quadrant is A, the left upper B, the right upper C, 

 and the right lower D.) 



Fig. 89.— Metaphase of third cleavage; spindles in definitive positions, second cleavage 

 sphere remnants still preserved at apical angles of cells. 



Fig. 90.— Anaphase and telophase of third cleavage : rotation of cell contents and bending 

 of spindle axes beginning ; second cleavage sphere remnants still preserved ; dual nuclei. 



Pig- 91. — Resting S cell stage ; rotation of cell contents and bending of spindle axes indi- 

 cated by relative positions of yolk, cytoplasm, mid-bodies, nuclei and centrosomes ; the latter are 

 chromatic and elliptical or spindle shaped. 



Pig 02.— Fourth cleavage and formation of second quartette ; third cleavage sphere rem- 

 nants at extreme left of each macromere, where they are spread into a broad ring by the upper 

 pole of the spindle ; centrosomes in micromeres spindle-shaped. 



Fig. 9:5. —Telophase of fourth cleavage of macromeres ; prophase of first division of first 

 quartette; the mitotic figure in one of these micromeres (la) has already begun to move from an 

 apical to a peripheral position in the cell. 



Fig. 94. — Slightly later stage than the preceding showing the extensive bending of the 

 spindle axes in the second quartette cells. Three of the first quartette cells are in the metaphase, 

 their spindles being in their definitive positions, the nucleus of the fourth (Id) is still in the apical 

 angle of the cell ; sphere remnants still lie in apical angles. 



Fig. 95. — Later stage than preceding showing still greater bending of the spindle axes of 

 the second quartette cells. In the first quartette three cells are in the anaphase, one in the meta- 

 phase ; third cleavage sphere remnants still preserved. 



Fig. 96.— Formation of third quartette : subdivision of second quartette, the sphere rem- 

 nants in these cells going into one daughter cell only (the right one) and not .into the other ; telo- 

 phase in division of first quartette, the nuclei showing dual character. 



Fig. 97. — Second division of first quartette ; the division in three of these cells (la, lb, Ic) 

 is unequal, in the fourth (Id) it is nearly equal and is always later than in the others. The ex- 

 tensive rotations in the daughter cells of the second quartette is indicated by the bending of the 

 spindle axes. The mesentoblast (4d) already formed. 



Fig. 98. — Resting 2(i-cell stage; the extensive bending of the spindle a.xes in the apical 

 cells is shown by the positions of the spheres, in the basal cells of the cross this bending is very 

 slight. A few dual nuclei are shown. 



Fig. 99. — Forty-one cells ; mesentoblast (4d) dividing ; the second subdivision of the second 

 quartette cells has occurred, the right product in each quadrant giving rise to the tip cell oi the 

 cross ; the third quartette has also divided, the direction of the division being Inotropic in quad- 

 rants A, B, C and slightly dexiotropic in quadrant D. 



Fig. 100. — Forty-five cells ; mesentoblast (-id) divided into right and left products (ME', 

 ME=) ; basal cells divided in three arms of the cross by a reversed cleavage ; the basal cell in the 

 fourth arm (posterior one) still undivided ; dual nuclei are shown in the tip cells. 



