and Fertilization in the Hemlock Spruce . 597 
nucleus into the egg-nucleus; but, even if the analogy were 
otherwise perfect, the increase in the amount of nucleolar 
substance seems to fully account for all the contents of the 
sperm-nucleus not found in its chromatic reticulum. 
The breaking down of the membranes separating the two 
nuclear cavities occurs before the completion of the spirem 
bands, but the chromatin masses remain distinct until the 
chromatic segments appear. The achromatic contents of 
the cavity, however, undergo a decided change, becoming 
denser and more fibrous in appearance with the probable 
rearrangement of the linin network under the stimulus causing 
division (Fig. 45). The outer membrane also disappears in 
places, and some of the cytoplasm presses into the cavity, but 
the chief activities of division are intranuclear. With the 
union of the nuclear cavities there also occurs a change in 
the cytoplasm of the egg. The dense sheath of small granules 
and fibres that encircles the unfertilized egg-nucleus partly 
disappears, and the larger cytoplasmic granules extend almost 
to the nuclear cavity, while the rows of elongated granules, 
radiating into the surrounding cytoplasm from the egg-nucleus 
since its origin, now lose their radial position and are dis¬ 
tributed without special arrangement. The indications are 
that the egg-nucleus has relaxed its hold for a time upon its 
cytoplasm to enter upon the changes involved in division. 
The fibres originating the spindle of the first segmentation 
arise among the segmenting spirems derived from the two 
nuclei, and they first draw together at several different points 
forming a multipolar spindle-rudiment. On these fibres the 
long bent and twisted chromosomes appear, still showing 
the chromatin disks distinct on the linin thread (Fig. 47). 
As the number of fibres increase, and the spindle becomes 
monaxial in form, the chromosomes contract and become 
homogeneous, and are mostly bent in the form of a U. 
There is no difference to be observed between the chromo¬ 
somes of the sperm and those of the egg, and, at this stage, 
they are mingled indiscriminately near the centre of the 
common spindle. 
