456 Prof. J. B. Farmer. On the [May 13, 



tended to upset this view, and to prove that just as the body itself is made 

 up of individual cells, each an entity in itself, so also, and even more emphati- 

 cally, the permanent elements of the nucleus are structurally distinct and 

 physiologically diverse. 



Eeduction or meiosis is no mere halving of the bulk of the chromosome- 

 substance ; its significance is to be discerned rather in the sorting out and 

 distribution between two daughter cells of the structural entities — the 

 primordia of characters — which are handed on from one generation to 

 another. 



We may now follow, as briefly as possible, the way in which the chromo- 

 somes behave during the meiotic divisions, and contrast the process with that 

 which obtains during an ordinary or somatic fission. 



In the first place it is observed that as the nucleus advances towards 

 division, and the chromosomes are able to be identified within it, their number 

 is only half of that characteristic of the nuclei of the preceding cell 

 generations that have arisen from the fertilised egg. A careful study of the 

 facts has shown that this reduction is as yet only a false one, and that the real 

 process is far more complicated. For each apparent chromosome is in reality 

 made up of two chromosomes which have become temporarily united together. 

 This union is, for a time, very intimate, and we have good grounds for saying 

 that it is not mere chance which determines which two particular chromo- 

 somes shall unite to form a pair. For example, it may happen that two 

 chromosomes in a premeiotic nucleus are different from the rest. Sometimes 

 there are several dissimilar pairs. At meiosis, the pairing always takes place 

 in such a way that like joins with like, to form the pseudo-chromosomes, as 

 these bodies have been well called. 



During the earlier stages, each of the paired chromosomes divides longitudinally, as in 

 an ordinary somatic division, but the two halves do not yet become separated from one 

 another. When the time comes for the splitting asunder of the two daughter-chromo- 

 somes to form the two nuclei, we find that the paired individuals now disunite and travel 

 apart. "When this has taken place, and the two daughter nuclei have been formed, the 

 longitudinal fission, to which I have already referred, finally takes effect, and the two 

 nuclei at once proceed to divide again. Each chromosome splits along the line of 

 cleavage already marked out during the previous division. The process essentially 

 resembles that of a somatic fission, but with this important difference, w., that the 

 reduced number of chromosomes is retained. And this feature continues to mark all the 

 nuclei of the post-meiotic cells, until the number is again doubled at the next act of 

 fertilisation. 



The net result of the meiotic phase is to effect the reduction in the number 

 of chromosomes, and hence of the chromomeres, by the device of distributing 

 half of the entire duplicated stock to one, and half to the other, nucleus. 

 I would remark, in passing, that this fact points to the conclusion that the 



