332 THOS. H. MONTGOMERY, 



(Figs. 185, 189, 192—198). Often the split first appears not as an 

 annular constriction, but as indentation of one end of the chromosome 

 (Figs. 186, 190, 193—198), and then usually of that end (distal end) 

 which points towards that pole of the spindle to which the chromo- 

 some is being pulled. An examination of the figures shows that the 

 split after metakinesis, even though at first it appears to be only a 

 constriction, corresponds in position exactly with the longitudinal split 

 of the early prophases of the maturation mitosis: it is placed per- 

 pendicularly to the axis of the transverse split of the bivalent chromo- 

 some ; and whereas the latter coincided approximately with the plane 

 of the equator of the spindle, the former is more or less at right 

 angles to this plane. In the early prophases the longitudinal split 

 was parallel to the long axis of the univalent chromosome; in the 

 monaster it is frequently absent, but in some cases is still marked 

 by a slight indentation at one or both ends of the chromosome; and 

 since in the metakinesis the split becomes clearly apparent, one may 

 conclude that, morphologically speaking, it had not disappeared in the 

 monaster stage but had simply become marked by a close approximation 

 of its edges. A consideration of these facts resolves the method of 

 determining how the two splits in the bivalent chromosomes lie with 

 relation to the another, into the following formulation : conceive the 

 two univalent chromosomes to lie in the same straight line, their 

 central ends joined by the central linin thread; then the latter thread 

 marks the transverse split of the chromosome, while in the long axis 

 of each univalent chromosome lies the longitudinal split. This relation 

 of the two splits to one another is actually maintained in chromo- 

 somes of the dumbbell form. But in those in which the two univalent 

 chromosomes lie parallel to one another, the longitudinal splits would 

 seem to be parallel to the transverse split. All my observations would 

 show that the split or indentation or constriction which appears in 

 the univalent chromosomes during the metakinesis and after, cor- 

 responds in position exactly with the longitudinal split of the early 

 prophase. And it is necessary that this point should be determined 

 with exactitude, for the split which appears during metakinesis comes 

 to coincide with the equatorial plane in the 2nd maturation division, 

 and so it is proven that the latter is an equational division. 



During metakinesis the pairs of centrosomes lie close to the cell 

 wall, and the pole fibres are very feebly developed. During this stage 

 the centrosomes have undergone a change in position: a line joining 



