76 W. B. Klrkham — Maturation of the Eyg of the 'White Motise. 



to be spherical (Text-figs. 2-3). It is larger than the second polar 

 body, and commonlj' measures from .022 to .028""° in diameter, 

 although the limits of variation are sometimes much greater than these. 

 Sobotta's statement that the first polar body in the mouse measures 

 only from .002 to .003""" in its larger diameter, is almost cei'tainly 

 based upon killed and stained material, while the figures here given 

 are the average of a large number of measurements of living eggs. 

 According to Rubaschkin (:o5), the guinea-pig has polar bodies 

 which measure from .012 to .01 7'""^ in diameter, and the egg of this 

 animal is practically of the same size as that of the mouse. 



The chromatin content of the first polar body consists of a vary- 

 ing number of masses, most of which are undivided dyads, com- 

 monly scattered through the cytoplasm, but sometimes in a spindle 

 (PI. VII, fig. 15), as seen by Tafani ('89) and Sobotta ('95) in the 



Figure 6. — Ovarian egg ; showing abnormal tri- polar spindle, x 675. 



Q^^ of the mouse, by van der Stricht (104) in a bat's ^^^^ and by 

 Rubaschkin (:05) in the Q^g2, of the guinea pig. Some of those 

 polar bodies which possess fully formed spindles would probably 

 have divided mitotically, and this is presumably the explanation of 

 the three polar bodies commonly found by van Beneden and Julin 

 ('80) accompanying bat's eggs. In PI. IV, fig. 8, an q^^ is shown 

 whose first polar body exhibits the telophase of mitosis; in PI. IV, 

 fig. 9, an example is given where the protoplasm of the jDolar body 

 is beginning to divide. 



The first polar body varies considerably in size in different eggs, 

 and in one series of ovarian eggs there are two with first polar 

 bodies of about four times the average volume (PI. IV, fig. 7). 



Two abnormal ovarian eggs have been seen (Text-figs. G-7) bear- 

 ing a striking resemblance to two observed by Rubaschkin (:05) in 



