The individuality of the chromosomes and their serial arrangement, etc. 125 



telophases they appear in contact with the nuclear membrane as soon 

 as it is formed and as the nucleus enlarges they move out with the mem- 

 brane. During early synapsis there is an indication of the attachment 

 of the leptoneme spirem to the membrane, and in diakinesis the paired 

 chromosomes again appear at the periphery of the nucleus. This be- 

 havior seems to indicate that there is some sort of organic connection 

 between the chromosomes and the nuclear membrane. 



The paired chromosomes are in some way carried toward the center 

 of the nucleus. The serial arrangement still persists and the chromo- 

 somes of a pair become so closely pressed together that there are few 

 which clearlv show evidence of their double nature. That they are double 

 is perfectly evident from their number as well as from a study of the 

 stages immediately preceding and following. Such a condition is shown 

 in figure 26. The behavior of the bivalent discrete spirem is entirely 

 similar to that of the single discrete spirem in the prophases of the somatic 

 divisions (compare figs. 25 and 26 with 10 and 11). 



As the nuclear membrane breaks down, the fibres extend into the 

 nuclear cavity and the bivalent spirem becomes flattened into the plane 

 of the equatorial plate. Neither here nor in the somatic divisions is there 

 such a shrinkage of the nuclear membrane upon the mass of chromosomes 

 as Lawson (1911 b) maintains is to be found in Disporum, Gladiolus, 

 Yucca, Hedera, and Allium. 



In a polar view of this stage the whole spirem is in view. The two 

 chromosomes of a pair can be identified when they lie in a profile view. 

 This is the position in which many are found during the early stages of 

 the heterotypic equatorial plate. Figure 27 shows this stage ; in this figure 

 there are thirty-seven masses of chromatin nearly all of which unmistake- 

 ably consist of paired chromosomes. It is possible that at least two of the 

 masses may consist of individual chromosomes which have either never 

 paired or have already separated. It is interesting to note that at this 

 stage one pair of chromosomes appears slightly larger than the rest. 

 No heteromorphic chromosomes have been observed at any previous 

 stage, yet in the polar view of the equatorial plate of the reduction divi- 

 sion this larger pair seems to appear quite constantly. The difference 

 is slight and the halves of the pair are apparently separated in the divi- 

 sion as are the others. 



The serial arrangement of the paired chromosomes is also strongly 

 suggested at this stage. When the distance between adjacent pairs in 

 different parts of the series becomes less than that between successive 

 pairs, it is often difficult to trace the spirem with certainty. Usually 



