650 
Beer. — S hcciies in Spore Development. III. 
One is at first tempted to conclude that each half of a longitudinally 
divided spireme segment condenses to form one of the two members of 
a bivalent chromosome, and therefore to consider that the heterotype 
chromosomes develop by a process of parasynapsis. 
This was the conclusion to which I first came and to which I gave 
expression in my former note. Since that article was written, however, 
I have had the opportunity of subjecting the phase of 4 second contraction ’ 
to a much closer scrutiny, and I have been successful in finding cases in 
which the entire course of events could be uninterruptedly followed from 
the stage of the longitudinally divided spireme segments (previous to the 
second contraction) up to the appearance of the fully developed heterotype 
chromosomes. 
The study of these unusually clear examples has shown that my former 
conclusions were erroneous, and that, instead of having an example of the 
parasynaptic origin of the heterotype chromosomes in Equisetum , this plant 
really furnishes a rather striking instance of their origin end to end. 
Before dealing further with the second contraction, it is first necessary 
to consider the appearance of the nucleoli in these nuclei during the pre- 
ceding stages of meiosis, as the peculiar behaviour of these bodies during 
the contraction adds no little to the confusion of that stage. In the resting 
nucleus, following the telophase of the last premeiotic division, a large 
number of medium-sized plasmatic nucleoli occur. It is not uncommon to 
find as many as eight nucleoli in a single such nucleus. Many of the 
nucleoli are spherical, whilst others are elongated, vermiform, or hour-glass 
shaped. Several forms are represented in Fig. 16. Some of these con- 
stricted nucleoli may possibly be undergoing division, but, in the light of 
what occurs a little later in their history, I believe that the majority of 
these hour-glass-shaped bodies are instances of nucleolar fusion rather than 
of their division. The outlines of these nucleoli are usually perfectly 
smooth, and it is only very rarely that any budding of material from their 
surface can be seen at this period. In older nuclei which are just about to 
pass into the synaptic contraction it can often be seen that the nucleoli, six 
to eight in number, approach one another and unmistakably fuse into a few 
larger bodies. 
In Fig. 14 it will be seen that on the left five nucleoli are grouped 
together but have not yet fused, whilst on the right of the nucleus three 
nucleoli have merged together into a' single vermiform structure which still 
clearly shows the points of fusion. Fig. 27 shows further nucleolar fusions 
at this stage. During synapsis the fusion of nucleoli is completed, and by 
the time the spireme has unfolded the nucleoli have been reduced to one or 
two comparatively large bodies (about 3 or 3*5 /x in diameter). That the 
single (or few) large nucleolus of the spireme is derived from the fusion 
and not from the partial absorption of the numerous nucleoli of the pre- 
