SI']G.ME,VTATIOX AXD DIFPEIIKNTIATIOX OP CHROMOSOMES. 285 
Transverse Segmentation and Internal Differen- 
tiation of Chromosomes. 
By 
W. E. 
Glasgow University. 
With Plates 12 and 13. 
The material for tliis paper was pai tly the same as was used 
for my former paper on the spermatogenesis of Lepidosireu , 
partly Lepidosireu larvae obtained during' the same expedi- 
tion, and pai'tly larvae collected by Prof. Graham Kerr on his 
previous expedition to the Pai'aguaj’an Chaco. 
SojiATic Mitoses. 
In my paper on the spermatogenesis of Lejiidosiren, it 
was shown that the univalents of the diakinesis of the first 
meiotic prophase develop a very marked transverse constric- 
tion. When tliese univalents ])air (i. e. the second pairing as 
described in the paper), the transversely constricted consti- 
tuents of each pair form together a perfectly typical “ tetrad.” 
As has now been found to be the case in so many forms, the 
four segments of each tetrad are not distributed to the four 
ganietes, but both divisions are longitudinal — that is, the 
transversely constricted chromosomes (‘Glyads ”) of anaphase 
I split longitudinally to form tetrads again, and anaphase II 
.separates chromosomes still transversely constricted as they 
were in prophase I. These transverse constrictions are left, 
therefore, without any assignable significance. Attention was 
drawn in the paper alluded to to the probability that the 
transverse constrictions correspond with the apices of the V’s 
