AND OF HYBRID PIGEONS. 
19 
the center of the sphere. In other words, the sphere is, then, 
only an active condition of the cytoplasm in a given region. 
The greatest visible change is in the nucleus itself at this 
period of disturbance in the primary spermatocyte. The 
chromatin drifts to one side and during its stay must undergo 
some sort of a profound alteration in its arrangement, for when 
the chromosomes reappear they are the double or bivalent type. 
It is possible, however, that we emphasize this phase of the 
phenomenon simply because it is the more visible through the 
great staining capacity of the chromatin. That the pseudore¬ 
duction may occur in reproduction cells without the accom¬ 
panying phenomenon of intra-nuclear collapse is well seen in 
the primary spermatocytes of the rat, where such a condensa¬ 
tion seems never to occur, although only half the original num¬ 
ber of chromosomes appears at the time, of division. 
In one or two instances it seemed very probable that during 
the internal changes of the nucleus quite enough chromatin to 
form a complete chromosome or more was ejected into the 
cytoplasm. At least two distinct examples were seen where 
there was a very tiny spindle connected with chromatin material 
lying in the cytoplasm at considerable distance from the main 
spindle. In one case, there was a single chromosome attached 
to the dwarf spindle, and in a second there was one large and 
one very small chromosome. Unfortunately the number of 
chromosomes at the equator of the main spindle could not be 
determined in these instances. It is interesting to note in this 
connection that the chromatin apparently determines the de¬ 
velopment of the spindle, for where we have enough chromatin 
accumulated to constitute a complete chromosome, it would 
seem that a spindle develops. Juel^ in a recent paper records 
an apparently similar occurence in the pollen-mother-cell of 
IlemerocaUis. On the other hand, the possibility exists, of 
course, that the small spindle may have been simply a readjust¬ 
ment of a part of the main spindle together with a chromosome 
which had become separted from it in some manner. 
1. Juel, H. O: Die Kerntheilungen in den Pollemutterzellen.—Jalirb. wiss. 
Bot.^ XXX, 1897. 
