tr] GATES—CHROMOSOME REDUCTION 341 
importance, but is merely a matter of cell mechanics; and the two 
methods of chromosome reduction are therefore essentially one. 
While the behavior of the chromosomes affords abundant evi- 
dence of some type of individuality or genetic continuity, yet 
there is no satisfactory evidence of any smaller unit of structure 
within the chromosome, and for this and other reasons there can 
be no hereditary difference between a parasynaptic and a telosynap- 
tic pairing of chromosomes. 
The one essential and probably almost universal fact of meiosis 
or reduction in sexual organisms is the segregation of whole somatic 
homologous chromosomes in the heterotypic mitosis. The reduc- 
tion process is everywhere the same in involving a segregation of the 
somatic chromosomes in the heterotypic mitosis, and a split of 
these chromosomes in the homotypic. — ; 
Since it is now known that the chromosomes are in homologous 
Pairs throughout the tissues of the sporophyte, this pairing must 
take place soon after the association in the fertilized egg of the two 
sets of chromosomes derived respectively from the egg and sperm 
nuclei. 
The fact that these homologous chromosomes are closely asso- 
ciated in pairs throughout the sporophyte, deprives synapsis of its 
supposed function of bringing about an interchange of materials 
or “influences” just before the chromosomes finally separate. 
If, as seems evident, the essential fact of meiosis is the mere 
Segregation and redistribution of the chromosomes whose ances- 
tors have been associated in pairs throughout the sporophyte, 
then the phenomena of the heterotypic prophase do not differ 
essentially from those of any somatic prophase. 
The unique condition of synapsis or synizesis is considered to be 
due, in some forms at least (for example, in Oenothera), to a sudden 
Srowth in the nucleus of the pollen mother cell without corre- 
sponding growth of the cytoplasm or of the nuclear reticulum. 
There appears also to be some contraction of the chromatic threads 
in the nucleus at this time, but the most important change is a 
rearrangement of the threads from the reticular to the spirem 
condition. 
The conspicuous appearance of “emptiness” of the synaptic 
