THE OVUM OF THE NINE-BANDED ARMADILLO. 123 



it is likely that follicular rupture takes place immediately after 

 the ovocyte has extruded one polar body; hence all of the cases 

 observed in which one polar body has been formed must be con- 

 sidered as ovocytes ready for ovulation. As a rule the first 

 polar body as it appears in ovarian ovocytes is much compressed 

 between the zona and the cell membrane, as in Figs. 38 and 41, 

 and is some distance from the second maturation spindle. This 

 position is, I believe, not to be interpreted as due to a migration 

 of the ovocytic nucleus in the interim between the two maturation 

 divisions, but rather as a shifting of the freed polar body. Ob- 

 servers of living mammalian ovocytes, notably Long and Mark 

 ('n), indicate that there is a considerable space between the 

 ovocyte membrane and the zona after the first polar body is 

 extruded. This space would offer the necessary conditions for 

 any shifting in the position of the polar body with reference to 

 the site of the maturation spindle. In Fig. 40 is shown a case 

 where the second polar spindle has established itself in close 

 proximity to the first polar body, in which the nucleus has re- 

 mained in a comparatively solid state. This is not a usual 

 condition, however, for in practically all other cases the first 

 polar body shows signs of a tendency to undergo mi to tic division. 

 I have never observed a well-defined spindle in a polar body, but 

 radiating fibers are always present and the chromosomes to some 

 extent divide and pass to tw r o poles of the cell, as in Fig. 38. 

 In only one case have I observed a complete division of the first 

 polar body and that is in a decidedly atypical case shown in 

 Fig. 42 and which is discussed in a subsequent connection. The 

 division of the first polar body must then be considered as merely 

 an abortive attempt at a division equivalent to the second 

 maturation division. It seems likely that the chromatin sub- 

 sequently goes back into a vesicular nucleus like that shown in Fig. 

 40, or like that in the fertilized egg shown in Fig. 44. 



The second polar spindle can be identified with assurance only 

 in ovocytes in w r hich the first polar body can be observed, and as 

 was indicated, these conditions are comparatively rare. Yet we 

 have several exceptionally good examples of such spindles, 

 notably those shown in Figs. 38, 39, 40 and 41. As a rule the 

 second spindle is noticeably smaller than the first, but the dif- 



