OF THE CJERM CELLS OF METAZOA. 



179 



pact structure and smooth outline. When it is beginning to elongate a faintly-marked 

 clear line can be seen in. its long axis (Figs. 125, 129), and this is evidently a longitudi- 

 nal split, comparable to that of the bivalent chromosomes; this split cannot be seen in 

 the telophase nor at any period of the maturation divisions. About coincident!)' 

 appears a, transverse split; this may be a. simple annular constriction, or a, clear con- 

 necting bridge of linin (as in Fig. 128). This transverse constriction, pointing to a 

 bipartite nature, would show that the chromosome x is bivalent; but it must have been 

 already bivalent in the spermatogonia, (where also a, transverse constriction can some- 

 times he seen, Fig. 123), for it does not unite with any other chromosome in the sperma- 

 tocytes. I can find no other explanation Cot its occasional bipartite appearance during 

 the synapsis. 



In the later period of the synapsis stage, in the telophase, and in the early prophases 

 of the first maturation division the chromosome x undergoes considerable changes in form. 

 The slightly bent rod (Figs. 125, 129) of the early synapsis bends at its middle point, 

 where the transverse constriction was apparent, into the form of a U or V (Figs. 120, 

 127, 130), or even the Conn of an 8 (Fig. 1275). The end result of these bendings seems 

 always to be a horseshoe-shape (Fig. 130) or a nearly closed ring ( Fig. 127 c). From the 

 early synapsis stage until the beginning of the prophases of the first: maturation mitosis 

 a true nucleolus of varying form is attached to the surface of the chromosome X (N, 

 Figs. 124, 125, 127-130); occasionally this true nucleolus may be separated into two or 

 three parts, all of them attached to the chromosome. In the prophases of the first 



maturation division the nucleolus becomes detached from the chromosome, rapidly 



decreases in size, and becomes lost before the nuclear membrane disappears. 



In the early prophases oC the first maturation division (Figs. 131, 132) are found 

 the following elements : (1) live bivalent chromosomes, of which all five are shown in 



Fig. L 32, only Cour in Fig. 133 (all these seen on lateral view); all these show at this 

 stage a well-marked longitudinal split (often of circular or oval outline) and a trans- 

 verse split (which marks the point of union of two univalent chromosomes); the mode 

 of formation of these elements is very similar to that- described by Paulmier (1899) for 

 Anam. (2) The bivalent chromatin nucleolus, the two parts of which may be in close 

 contact (N. 2, Fig. L32) or may still be widely separated {N. ::', Fig. 131). And (3) 

 the Laree chromosome x, the Largest of all the elements, which now has decreased some- 

 what in volume owing lo the greater condensation of its substance; seen from the side, 

 it gives the appearance of a, thick horseshoe or a nearly closed ring (x, Fig. 131). Of 

 the live bivalent chromosomes, one is always much larger than the Others {K. -2, Figs. 

 131, L32), and this was evidently formed by tin; union of the two large chromosomes 

 A" of the spermatogonic mitoses (Figs. 1 L9— 123). 



