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 Abietineas. 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 always 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 Stages in the Mitosis. During 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 fig. 237. Itas 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- 



