SINGLE AND DOUBLE, RINGS. 



359 



apposed points of constriction of the homologues, and is pulled 

 out by the spindle fibers towards each pole, pulling the chromatids 

 out of the rings or V's as it apparently increases in size at the 

 expense of these rings or V's. In Fig. 3, bivalent I. consists of a 

 large loop with two medium-sized rings; one of which is seen 

 edgeways. This ring shows the division into chromatids. This 

 bivalent perhaps started as two rings. In Fig. 5, lower line, 



FIG. 4. Bivalents from two more selected cells showing the metaphase to 

 anaphase, as in Fig. 3. Two bivalents, VI. and VII., are of the exceptional 

 form. 



bivalent I. consists of a diminishing ring and a V, with a large 

 loop between them, formed probably at their expense. Bivalent 

 I., in the upper line of this figure, is apparently similar but the 

 ring is somewhat bent. In Fig. 3, of the paper on the origin of 

 mutations, bivalent I. has the form of a large loop with two small 

 rings, probably remnants of original large rings. In Fig. 4 of 

 the present paper, upper line, bivalent I. has a ring on one side 

 of the loop, while on the other side the ring may perhaps have 

 been vertical, and the two halves have separated vertically. In 

 the lower line of this figure, the halves of bivalent I. have sepa- 

 rated at one end, but the last remnant of the V remains at the 

 center. Finally, in Fig. 6, the 4 chromatids of bivalent I. are 



