144 T - H - MONTGOMERY, JR. 



are different in form from others, just because they represent 

 pairs of univalent chromosomes. If they arose by simple longi- 

 tudinal splitting, why should they differ so in form from the 

 chromosomes of the spermatogonia, or of the spermatocytes of 

 the second order ? 



And here my thanks are due to Janssens and Dumez for this 

 critique of my interpretation, because it induced me to study 

 anew the amphibian spermatogenesis, and this reexamination 

 brought out the fact, strong in support of my position, that the 

 chromosomes are regularly paired in the spermatogonia. 



2. THE INDIVIDUALITY OF THE CHROMOSOMES. 



By the idea of the maintenance of the chromosomal individu- 

 ality we do not mean that a chromosome remains chemically 

 unchanged from generation to generation (for after every mitosis 

 a daughter chromosome grows to the size of a mother chromo- 

 some before it divides in the next mitosis), but that, despite great 

 metabolic and structural changes, a chromosome of any generation 

 is the descendant of a particular chromosome of the preceding 

 generation, and is not a new formation. A chromosome of one 

 generation represents a chromosome of a preceding, just as much 

 as a cell of one generation represents a particular cell of a pre- 

 ceding generation. This idea was first propounded by Rabl, 1 and 

 has steadily gained in support. The workers on ovogenesis 

 have, for the most part, taken the position that it is not proved ; 

 but the reason there is simply the great duration of the growth 

 period of the ovocytes, during a part of which chromosomal 

 boundaries are not distinguishable. The students of spermato- 

 genesis, on the other hand, are fairly unanimous in support of 

 the view. 



It is very important that this idea should be firmly established, 

 and certain considerations would show it to be so. There is first 

 the fact that from generation to generation the number of chromo- 

 somes remains the same, from the stage of the fertilized egg to 

 that of the ovocyte or spermatocyte of the first order. Even the 

 form of the chromosomes is maintained through these generations, 

 as shown in the case of the cleavage of Ascaris. In the sperma- 



1 " Ueber Zelltheilung," Morfliol. Jahib., 5, 1885. 



