tort] | GATES—CHROMOSOME REDUCTION 325 
resting nucleus to the compact condition of the prophase, any par- 
ticular arrangement of differential units of structure composing an 
individual chromosome takes place. 
Studies of forms whose chromosome group is composed of 
bodies morphologically unlike (heteromorphic) have shown, for 
example in various insects, that the chromosomes frequently 
maintain the same space relationships to each other in each equa- 
torial plate, and therefore also probably during the intervening 
“resting” conditions of the nuclei. Other clear evidence, given, 
for example, by Bovert (1 and 1a), leads to the same conclusion. 
Hence it is probable that the direction of the long axis of the 
chromosomes, and hence their plane of division, correspond in 
Successive mitoses. It does not therefore follow, from the state- 
ments of the last paragraph, that there is no difference between 
a longitudinal and a transverse division of a somatic chromosome. 
For even though such a transverse fission may be of no hereditary 
Significance in separating unlike parts of a chromosome, yet it 
may have an important mechanical significance, and as far as the 
morphology of the product is concerned, the result of a transverse 
split of certain chromosomes in a nuclear plate may very well 
be different from that of a longitudinal fission. STRASBURGER 
(25, p. 437) Suggests as an explanation of the heteromorphic chro- 
mosomes in such forms as Funkia, Yucca, and Galtonia that the 
short chromosomes have arisen by the transverse segmentation 
of certain of the long chromosomes. This may have been a conse- 
quence of the differentiation of the parts of such chromosomes, or 
may have resulted from more purely mechanical causes, but at 
any rate it furnishes no evidence that successive longitudinal seg- 
ments of the long chromosomes which maintain their unity are 
unlike.3 Therefore, although, phylogenetically considered, trans- 
verse segmentations of members of the chromosome group have 
doubtless occurred in various species, it does not follow that these 
segmentations have any fundamental hereditary significance, 
*In a few forms, such as Ascaris, having very few chromosomes, they appear to 
be compound structures, as shown by their fragmentation in somatic mitoses; but 
In the great majority of forms no evidence of the compound character of the chromo- 
Somes is forthcoming. 
