SO-CALLED PARTHEXOGEXESIS IX THE WHITE MOUSE. 243 



spindle, but are scattered in the plane through the middle of the 

 spindle, at right angles to its length. The chromosomes of the 

 first polar spindle are larger than those of the second and are 

 long with a marked thickening or swelling at the middle. This 

 thickening is at one side of the chromosomes and it is at this 

 point that division takes place. The division is apparently 

 transverse. This account agrees with those of Sobotta and 

 Kirkham for the normal first maturation spindle. 



The chromsomes are grouped so closely together and overlap 

 to such an extent that it is difficult to determine their number 

 with accuracy. They apparently vary in number from twelve 

 to twenty-four, the larger numbers being due to a precocious 

 division of some, while others are still undivided. 



Descriptions of the appearance of the spindle itself differ. 

 Sobotta, Kirkham, and Lams and Doorme, state that polar 

 radiations or asters are not present in first polar spindles of 

 normally maturing oocytes, and Athias agrees with them in the 

 case of degenerating egg-cells. Rubaschkin, however, describes 

 in atretic oocytes of the guinea-pig polar radiations arising from 

 a clear area or centrosphere. Kirkham describes centrosomes 

 consisting of several minute granules at the poles of the spindles. 

 Sobotta states that there are no centrosomes in the first polar 

 spindles of normally maturing oocytes, and Athias finds none in 

 degenerating egg-cells. In my own preparations radiating fibers 

 are to be seen at the poles of a few first polar spindles; these, 

 however, are not to be considered true asters, but spindle fibers 

 which have broken away from the spindle. This will be discussed 

 more in detail further on. No centrosomes are found in any of 

 these degenerating oocytes. The spindle fibers are not divided 

 into central spindle fibers and mantle fibers; the fibers with 

 chromosomes attached are intermingled with those which are not 

 connected with chromosomes. The two kinds do not differ in 

 appearance or staining reaction. The spindle itself usually lies 

 at right angles to the radius of the oocyte, until it swings around 

 to a radial position for the formation of the polar body. (See 

 Figs, i, 2 and 5.) 



The stages in the formation of the first polar body must 

 follow one another rapidly for only a few of these stages were 



