PLATE 15 



EXPLANATION OF FIGURES 



73 (1089) Centrifuged 100 turns of hand machine, fixed 4 and 6 liours 

 later. First cleavage (7) equatorial; second meridional in cell below equator, 

 oblique and belated in cell above the equator. 



74 (1139, 1) Centrifuged 2^ hours at the close of the first cleavage, fixed 

 at once. In the right half of the egg, cytoplasm and nuclear spindle were dis- 

 placed toward the vegetal pole and were held in that position during the second 

 cleavage; therefore the second cleavage furrow in the right half is nearly equa- 

 torial in position and in both daughter cells the centrospheres lie on the animal 

 pole side of the nucleus. In the left half of the egg division is nearly normal, 

 though somewhat belated. 



75 (1136,5) First polar body missing. The second polar body (with two nuclei) 

 contains oil and cytoplasm and was therefore extruded at centripetal pole, which 

 was near vegetal pole of egg. Cytoplasm and nuclei did not return to animal 

 pole before the first cleavage (/-/) which was equatorial, consequently cyto- 

 plasm and nuclei were cut off in cells below the equator. Positions of cytoplasm, 

 nuclei and spheres show that the animal pole {AP) is at top of figure. The posi- 

 tion of the cytoplasmic areas in the different cells, as well as that of the mid- 

 body and the spindle remnants, prove that furrow running from the top to the 

 bottom of the figure is the second cleavage but the spiral direction of this cleav- 

 age is dexiotropic, as shown in the position of the cells and by the polar fur- 

 rows, whereas in normal eggs this cleavage is laeotropic. 



76, 77 (1035) Centrifuged 30 minutes, fixed 3 hours later. The first cleavage 

 (7) was equatorial, the second (77) meridional. Each macromere is giving off in 

 a dexiotropic direction and as near as possible to the animal pole, a micromere 

 of the first set. 



78 (1151) Centrifuged 5 hours, fixed 5 hours later. The first cleavage was 

 equatorial, the second meridional. Each macromere has formed a micromere 

 of the first set and the two macromeres below the equator have also formed the 

 second set of micromeres {2c, 2d) ; the macromeres above the equator are in proc- 

 ess of giving off the second set of micromeres. 



402 



