DEVELOPMENT OF THE ALBINO RAT 11 



The phenomena of maturation and fertilization in the albino 

 rat have been carefully studied by Sobotta and Burckhard, 

 from whose account the following brief summary is taken: The 

 behavior of the ovum of the albino rat with respect to the forma- 

 tion of polar bodies is very similar to that of most other mammals 

 studied. The first polar body is given off within the ovarian 

 follicle, the second in the oviduct and only after semination. 

 The first maturation spindle, developed from the nucleus of the 

 oocyte of the first order, forms usually immediately after par- 

 turition. Kirkham and Burr state "it is usually formed less 

 than 24 hours after parturition." It is short and broad, with 

 the chromatin scattered. The first maturation spindle lies near 

 the center of the ovum, then passes toward the surface assuming 

 a tangential position, and only with the beginning of metakinesis, 

 takes a radial position. The chromosomes of the first maturation 

 spindle, estimated as numbering 16, appear in the form of modified 

 rings, which are divided transversely across to form short rounded 

 rods with a longitudinal direction in the diaster stage. The 

 first polar body is formed in the ovarian follicle and appears 

 to be relatively large. It is evident only in the ovarian ovum, 

 and appears to be lost soon after its formation. Its fate is 

 doubtful. The first polar body is nearly always missing in tubal 

 ova. Kirkham and Burr state that "the rare occurrence of 

 the first polar body associated with the egg in the tube is to be 

 attributed to its rapid disintegration, which begins as soon as it 

 is formed, and may lead to complete disappearance before 

 ovulation occurs." The second maturation division begins 

 immediately after the completion of the first, without an inter- 

 vening resting phase. The spindle formed is narrower and 

 longer than the first, with the chromatin massed. In its monas- 

 ter stage, it lies in a tangential position, with the chromatin 

 in diads, and with the lines of division at right angles to the 

 axis of the spindle. The appearance of the second maturation 

 spindle in the monaster stage marks the end of the maturation 

 phenomena in the ovary. The monaster stage of the second 

 oocyte division was not observed in the ovary by Sobotta and 

 Burckhard, but was seen by Kirkham and Burr. The first 



