990 J. E. S. MOORE. 
ever the case in either Elasmobranchs or newts, in both of 
which the loops lie flat, with both limbs on the spindle surface. 
As the loops lengthen out towards the poles, the outward 
bends are gradually reduced, but they never disappear, and at 
the time the chromosomes divide (fig. 47) they separate from 
one another in such a way that the original openings of the 
loops are clearly seen, The separation into daughter-elements 
is effected by a transverse splitting of the loop across the central 
thickening, at right angles to the then long axis of each 
chromosome (fig. 47), as is usual in Heterotype metores. 
After their separation, the daughter-chromosomes form super- 
ficial chromatic rings (fig. 48—51), as did those in the divi- 
sions of the first spermatogenetic period (see § 13), and the 
spindle-fibres in like manner become differentiated into two 
concentric tubes, separated from one another by the nuclear 
sap. This differentiation of the spindle into fibrous tubes is 
carried further than in the divisions of the first spermatogenetic 
period, the whole structure appearing to be composed of two 
completely closed cylinders of fibres, one (fig. 49, 0. s.) stretched 
directly between the outer edge of the chromatic rings, and 
the other (¢.s.) passing internally through them to the centro- 
somes. The unstained fluid which separates the outer from 
the inner of these sheaths, is that which previously filled 
the interspaces between the fibres of the younger spindle, and 
it was once the parental nuclear sap. It contains irregular 
chromatic granules (0. ¢., fig. 50) which appear to have been 
left as débris of the chromosome formation, and which sooner 
or later pass into the cytoplasm of the cell (0.c., fig. 54). 
29. While the above changes are in progress, the centro- 
somes become surrounded by the dusky zone, created by the 
shortening up and coalescence of the cytoplasmic fibres between 
them and the chromosomes (figs. 48, 49, 50 a). 
30. The chromosomes of each daughter-nucleus are at this 
time quite separate and distinct, although lying closely side by 
side; but as time goes on they begin to fuse together, so that 
the chromatin eventually forms two solid chromatic rings, one 
in each daughter-cell (figs. 51, 52, 53). 
