W. B. Kirkham — Maturation of the Egg of the White Mouse. 75 



No radiations from these, however, such as have been described by 

 Bellonci ('85) for the mouse q^^ and b}'- van der Stricht (:o6) for 

 a bat's egg, have been seen by the writer. As might be expected 

 from its larger chromatin content, this spindle is usually longer and 

 broader than the second, a point noticed by Gerlach (:o6), but it 

 varies in size at different periods of development. The first matura- 

 tion spindle is also larger than the second spindle in the eggs of most 

 of the invertebrates. 



After remaining for a time in the paratangential position, one pole 

 of the first maturation spindle moves toward the center of the qq^^ 

 (PI. II, fig. 4), as seen by Sobotta ('95), while the other presses 

 against the outer surface of the Q^^. These movements are prepar- 

 atory to the extrusion of the first polar body. 



4/ 



^Vf 



Figure 5. — Diagram of chromosomes in first polar spindle of the ovarian egg 

 shown in PI. I, fig. 2. On the right two large quadrivalent chromosomes 

 are seen before splitting. To the left of these are three pairs of bivalent 

 chromosomes, which have completely separated, while near the middle of 

 the figure occurs another quadrivalent chromosome. At the left of the 

 diagram are seen eight additional chromosomes differing greatly in size, 

 while four more similar masses of chromatin appear in adjacent sections. 



First Polar Body (PI. Ill, figs. 5-6).— The first polar body in 

 the %^g of the mouse, as far as observed by the writer, is always 

 formed within the ovary in every ^^^, which matures. A large num- 

 ber of eggs in different ovaries have been examined, and in every 

 instance where the size of the ^^^., its slightly denser protoplasm, 

 and the large follicle gave evidence of ripeness, the Q^'g was found 

 to be accompanied by the first polar body. This agrees with the 

 observations of Bellonci ('85), and with Sobotta's idea regarding 

 ten per cent, of the eggs, which he believed formed two polar bodies; 

 it is also in accord with the work of van der Stricht (:0I, :o6) on 

 the ^^^ of Vesperugo noctula, and that of Rubaschkin (:05) on the 

 egg of the guinea-pig. 



In the mouse the first polar bod}' is oval in form when seen in 

 sections which have been killed and stained, but in life it is more apt 



