CHANGES IN REPRODUCTIVE CELLS OF ELASMOBRANCHS. 281 
well-known open ring-form of the diastral figure represented 
in fig. 24. 
12. In consequence of this outward motion of the inner 
chromosomes, the spindle (now intra-zonal) fibres with which 
they are connected become drawn out from their original 
axial position, and form a central fibrous tube (fig. 24, 7.8.) 
enclosed by (i) the remains of the nuclear sap, (ii) the external 
spindle (intra-zonal) fibres (0. s.), and (iii) some linin fila- 
ments left stretched between the separate chromosomes, which 
last, in my opinion, represent the true! “ Verbindungsfaden.” 
The “ Verbindungsfaden”? and the intra-zonal fibres now 
become indistinguishably fused, while the differentiation of 
the achromatic spindle into an inner and an outer sheath, 
becoming more distinct, gives to that structure the appear- 
ance of two concentric tubes, one of which (0. s., fig. 24) is 
stretched directly between the outer edge of the chromatic 
rings, the other (@. s., fig. 24), passing internally through 
them, to its termination in the centrosomes. The unstained 
fluid which separates the outer from the inner of these 
sheaths is that which previously filled the interspaces- be- 
tween the younger spindle-fibres, and it was once the 
parental nuclear sap. It contains a few irregular chromatic 
particles (fig. 24, b. c.), which appear to have been left as 
débris of the previous chromosome formation, and which 
sooner or later pass (fig. 26, 6. ¢.) into the cytoplasm of 
the cell. 
While the above changes are in progress the centrosomes 
become gradually surrounded by a dusky zone (figs. 20, 26, 27), 
which is caused by the shortening up and coalescence of the 
cytoplasmic fibres between them and the chromosomes, 7. e. by 
those described above (§ 8) as structurally equivalent to 
Hermann’s mantle. 
13. The chromosomes in the two daughter-rings (fig. 24) 
are at first quite distinct from one another, although lying 
closely side by side, but as time goes on they fuse together, 
1 See Ishikawa, “Studies of Reproductive Elements; Noctiluca,” ‘Journ. 
Sci. Col. Imp. Univers. Tokio,’ vol. vi, p. 322. 
