SEGMENTATION AND DIFFERENTIATION OF CHIiOMOSOMES. 295 
chromosomes as a wliole.^ The permanent forms of meiotic 
chromosomes found in certain animals by Moore and Arnold, 
and by Walker, may reasonably be supposed to be due to the 
same lengthwise differentiation. 
Finally, the facts here described are plainly in favour of 
the theory of chromosome individuality. Quite recently 
Meves has attacked this theory, largely on the grounds that 
chouo:h size dilferences exist amonjjst the chromosomes of the 
salamander, yet individual variation, and unavoidable distur- 
bances due to bending, foreshortening, etc., are so great as to 
make impossible the constaut identification of the same 
chromosome. He is also sceptical of the possibility of arrang- 
ing the somatic chromosomes in pairs. Sucli negative evidence 
as his cannot, however, be held to counterbalance positive 
evidence gained from those forms in which the size and other 
dilferences are great enough to appear through all disturbing- 
factors. This is certainly the case with, at any rate, the lai-ge 
pair of chromosomes in Lepidosiren. 
Summary. 
(1) The tendency for chromosomes to become transversely 
segmented or constricted is a wide-spread characteristic. It 
becomes operative especially, but not solely, whenever the 
chromosomes are short in comparison with their length, as 
happens normally in meiosis, and exceptionally in somatic 
tissues. 
(2) The point at which the constriction or segmentation 
takes place in any given chromosome is constant for that 
chromosome, and is the same as the point at which it most 
readily bends to form the angle of the V when present in 
that form. 
' Acceirting the commonly held views as to chromosome individuality 
and reduction. Those who would hold the opinion that the scattered 
chromosomes of the meiotic prophase ar-e not whole chromosomes, but 
precociously sei^arated daughter halves, have still to explain the fact 
that when they come together again on the equatorial plate, like ends are 
always applied to like. 
