26 EDWARD MCCRADY, JR. 



At the end of this time all chromosomes show signs of de- 

 generation, and the egg undergoes irregular fragmentation 

 without mitosis. 



If fertilization has occurred, the second maturation division 

 giving rise to the second polar body takes place. In the 

 normal metaphase of this division there are at first eleven 

 diads; but the X-diad often divides precociously, so that 

 spindles are frequently found showing ten diads and two 

 monads. This led Hartman ('19, p. 35) to the conclusion 

 that the haploid number of chromosomes is twelve. Painter 



Fig. 6 Early tubal ovum (16266). Albumen is just beginning to be deposited 

 on the- zona. There is still only one polar body. The organization of the cyto- 

 plasm into a shallow, peripheral, homogeneous, darkly -staining zone; a sub- 

 peripheral, irregular, yolk-laden zone; and a broad, homogeneous, lightly-staining, 

 central zone; is well shown. The yolk granules are larger than they were in 

 the ovarian ovum. 



( '22, p. 35) after a study of spermatogenesis, where a parallel 

 precocious splitting of the sex chromosome often occurs (v, 

 fig. 2, B), noted this mistake and corrected it. 4 



The two polar bodies are visible in many of the very early 

 cleavage specimens. Hartman ('19) has seen what he in- 

 terprets as polar bodies as late as the 34-celled stage; but 

 usually one finds them difficult to recognize after the second 

 cleavage on account of the phenomenon of yolk extrusion, 

 which will be described below. 



4 To anyone interested in the source papers one further explanation is necessary. 

 At the same time that Painter corrected Hartman 's original mistake he in- 

 advertently introduced another which makes his account somewhat puzzling. He 

 consistently refers to the diads in Hartman 's figures of second maturation divisions 

 as tetrads, and to the monads as diads. I have pointed this out to him in 

 conversation, and he agrees that it was a slip of the tongue. 



