226 The Botanical Gazeite. [May, 
fibres are continuous from pole to pole was due to insufficient 
knowledge of the facts. The difficulty has been cleared up 
by the pretty general acceptance of the view that there are 
formed in some cells, such as the spermatocytes of the sala- 
mander, continuous spindle-fibres reaching from pole to pole, 
and, outside of these, groups of peripheral fibres which reach, 
at farthest, only to the equator of the spindle; while in other 
cells, including the egg of Ascaris megalocephala, only these 
peripheral fibres, and none of the central spindle, appear to 
be formed. Hermann and Driiner derive the central spindle, 
where it has been observed, from the substance connecting 
the centrosomes. It appears at first very small and grows as 
the centrosomes separate. A somewhat similar phenomenon 
is described by Lauterborn (11) as giving rise to a spindle- 
like structure in one of the diatoms. This observation 
quent retraction of the peripheral fibres. These are believed 
to grow outward from the centrosomes, attaching themselves 
to the chromosomes and pushing these before them until they 
reach the equator, where fibres from opposite poles become 
attached to the respective halves of each chromosome. Now 
begins the contraction of the fibres, which results in the 
separation of the daughter-chromosomes and in their being 
drawn finally to the poles, on the complete retraction of the 
peripheral fibres. Driiner (4) also attributes the migration 
of the centrosomes to the poles of the nucleus to the push of 
the fibres seen radiating from them at this time, against cell- 
wall and nucleus, their paths being determined by the result- 
ants of all the pushes to which they are exposed. Many 
zoologists, with this writer, regard the centrosomes as mere 
points of attachment for the kinoplasmic threads. 
