Il8 MARGARET C. FERGUSON 



be distinguished (fig. 234). One beautiful preparation was ob 

 tained at this stage in which a single section through the nuclear 

 plate showed twenty-four entire chromosomes, and no chromo- 

 somes were found in the other sections of the series (fig. 235). 

 As twelve chromosomes had previously been counted in the egg- 

 nucleus there can be little doubt that the same number is brought 

 into the egg by the sperm-nucleus. So far as form and struc- 

 ture are concerned the twenty-four chromosomes of this prepara- 

 tion are exactly alike, and at this stage I was no longer able 

 to distinguish between the maternal and the paternal segments. 



The smallness of the mitotic figure in the first division fol- 

 lowing fecundation compared with the size of the egg-nucleus 

 has been commented upon by Strasburger ('92) and by all later 

 students of the Abietineee. This spindle may occupy various 

 positions in the space originally filled by the egg-nucleus, but, 

 as is clearly demonstrated by a study of its development, it 

 invariably lies partly within the sperm- and partly within the 

 egg-nucleus, its major axis being alwa3^s parallel with the outer, 

 free surface of the sperm-nucleus. While, then, the karyo- 

 kinetic figure bears a certain definite, fixed relation to the con- 

 jugating nuclei, it will be readily seen that its position may 

 vary, depending upon the shape of the sperm-nucleus and its 

 line of contact with the egg-nucleus, as, also, upon the plane at 

 which the section is cut with regard to the sexual nuclei. For 

 instance, when the sperm-nucleus is elliptical in outline and lies 

 in a deep depression in the egg-nucleus, as illustrated in figs. 

 221 and 223, a, plate XX, the spindle will appear to occupy the 

 center of the egg-nucleus. Cases like the above and many 

 others were first satisfactorily interpreted after a careful study 

 of something like two hundred preparations showing fertiliza- 

 tion stages. 



Later Staores in the Mitosis. — Durincj metakinesis the 

 mitotic figure may present every variation between the ex- 

 tremely broad, multipolar diarch, shown in fig. 236, and the 

 narrow, almost bipolar spindle, illustrated in '^^g. 237. It is at 

 this time that the longitudinal splitting of the chromosomes first 

 becomes apparent. Each chromatic element divides at the point 

 where the spindle-fibers are attached, forming a small diamond- 



