223 
Pollen Mother-cells of Lilium canadense . 
were noted in the equatorial plate appear during their separation. At 
a and a ! , Fig. 107, appear two, evidently sister chromosomes, showing 
a form intermediate between that of a hooked rod and a V ; and at b and b' 
(same figure) are two V-shaped sister chromosomes, each having one arm 
somewhat shorter than the other. Similar forms appear in later stages 
in the separation of the chromosomes, and during their passage toward the 
poles. . 
As the chromosomes approach the poles, they become considerably 
straightened out, the rod-shaped ones then often reaching nearly from the 
pole to the equator. After reaching the pole, however, they seem to become 
shorter and thicker (a process which was also noted in the previous division). 
The equatorial ends then become curved, and finally all the chromosomes 
are bent and closely compacted together. The extra-nuclear nucleoles, 
which were numerous in the prophases, become less numerous, and fre- 
quently almost entirely disappear by the time of the formation of the 
mature spindle. They reappear, however, in considerable numbers during 
the separation of the daughter chromosomes, and at first are especially 
numerous in the equatorial region. After the formation of the cell-plate, as 
in the preceding division, they gather in the neighbourhood of the reforming 
daughter nuclei, and often some of the smaller ones seem to fuse into larger 
bodies. The reconstruction of the daughter nuclei is closely parallel to the 
corresponding process in the preceding division. 
Discussion. 
The Visible Idioplasmic Structures . 
It is well established that in both plants and animals, as first shown by 
van Beneden (’83) for Ascaris , the union of the sexual nuclei involves 
no fusion of their chromosomes ; the latter pass, apparently unchanged, 
into the fusion nucleus. We must also, as the case stands at present 
(see Boveri, ’04), accept the notion of the general persistence of individual 
chromosomes, and the consequent reappearance in the division of any 
somatic nucleus of the same chromosomes which were present in the 
anaphases of the division immediately preceding. New evidence of this 
general fact, derived from a study of plant nuclei, has recently been 
published by Rosenberg (’04 c). 
The acceptance of the doctrines just stated involves the further notion 
that the chromosomes received respectively from the germ-cells of the male 
and female parents remain separate throughout the life-history of the 
offspring. Every nucleus of the new generation is therefore double, in the 
sense that it contains two uncombined sets of chromosomes, and therefore 
