SEOMEXTATIOX AND mFEEREXTIATIOX OF CHROMOSOMES. 291 
tried to arraiio’e tlie cliroinosoines roughly in order. The 
large pair, or large tetrad, can nearly always be easily recog- 
nised, but the gradation in size amongst the remainder is so 
continnons, and disturbances due to foreshortening, etc., so 
inevitable, that it is impossible to attain to accuracy of 
arrangement. Fortunately for onr purpose, however, while 
the large pair of chromosomes always segments approximately 
symmetrically, at least the next four pairs in size segment 
very unequally. Hence, confining our attention to the few 
largest pairs only, we can see that among them at least the 
angles of the V’s or transverse constrictions of the tetrads 
alwiiys occur in the same region of any given chromosome. 
While it is not possible to be sure of the identification of all 
the other chromosomes, an examination of the figure leaves 
little doubt in one’s mind tliat the same constancy holds for the 
smaller chromosomes also. This impression is gathered still 
moi-e stroiiLdy from the preparations themselves, in which it 
is easier to allow for irregularities due to foreshortening’, etc. 
The equality of the segments of the pair of large chromo- 
somes and iiieqnalit}' of tliose next in size is shown incidentally 
in figs. 24-dl of my former paper. 
Another important fact brought out by a study of the 
meiotic figures is that in the asymmetrical tetrads like ends 
are always applied to like. [That is, the small segment is 
applied to small and large to large]. In the case of the 
somatic tetrads this orientation follows from their mode of 
formation. The case of the meiotic tetrads is different. As 
described in my former paper, at the time that the transverse 
constrictions are developed, the chromosomes may be lying 
widely scattereil thi'ough the nucleus. Hence the juxta- 
position of like ends to like when they pair to form the 
definitive tetrads must be put down to an active cause. 
Literatcee. 
Many c}'tologists have noted the occasional occurrence of 
tetrads ” or transversely segmented chromosomes in somatic 
