STRUCTURE OF CERTAIN CHROMOSOMES 19 
Part II. Division. 
(a) Historical. 
It was made out by Flemming in 1880 that the chromosomes 
of the equatorial plate are double, that is, composed of two 
similar longitudinal halves, closely approximated. The parallel- 
ism and close approximation of these halves naturally suggested 
that they arise by a longitudinal splitting of a previously 
undivided mother chromosome; and this suggested inquiry 
as to the means by which the supposed splitting could be 
brought about. 
In 1881 Pfitzner’ put forth a schema of this splitting which 
seemed plausible and met with general acceptance. According 
to this, the mother chromosomes are composed either of a single 
row of globular granules of chromatin, of a diameter exactly 
equal to that of the chromosome and embedded in an achro- 
matic matrix ; or of a double row of such granules, of only 
half the size of those of the single row. These double rows 
are sometimes very closely approximated, sometimes less 
so; and finally separate from one another as daughter 
chromosomes. The ‘splitting’ of the mother chromosome 
would thus seem to be brought about by the binary division 
of each of its constituent ‘ granules ’. 
This theory won ready acceptance; and the supposed 
‘granules ’, under the names of ‘ Pfitzner’s granules ’, ‘ micro- 
somes ’, ‘chromomeres ’, ‘chromioles’, and the like, are still de- 
seribed and believed in and made the basis of much fanciful 
explanation. 
According to my own very extended observations, this notion 
of the ‘ splittmg ’ of chromosomes being brought about by the 
splitting of their component ‘ chromomeres’ is baseless. For 
no such granules exist at any time. It is abundantly clear to 
me that all the appearances that have been described as 
1 « Uber den feineren Bau der bei der Zelltheilung auftretenden faden- 
formigen Differenzirungen des Zellkerns ”’, in ‘ Morpholog. Jahrbuch ’, vii, 
p. 289—a much quoted but rather wretched performance, 
C2 
