70 THOS. H. MONTGOMERY jr., 



Heuce, we must take as the representative of relatively normal 

 (primitive) mitoses the adult tissue cells, the spermatogonia and ovo- 

 gonia. We must see how the term chromosome is apphed in these 

 cases, and then apply this definition to the chromatin elements of the 

 reduction divisions, in order to determine the value of the latter. 



In adult tissue cells, spermatogonia and ovogonia, a chromosome, 

 as the term is generally used, there may be resolved into the follow- 

 ing definition. A chromosome is each separate chromatin element 

 (chromatin microsomes imbedded in, or sheathed by, linin) formed in 

 the prophases of mitosis by transverse segmentation of the spirem 

 thread, or which, in those cases where a continuous spirem is not 

 formed, segregates as a separate element from the chromatin reticulum 

 of the resting cell ; the halving of each chromosome in metakinesis re- 

 sults in the formation of two daughter elements, each of which has the 

 value of a chromosome only in the daughter cell in which it comes to 

 lie, — that is to say, metakinesis doubles the number of chromosomes. 

 In cases where division of the chromatin of a chromosome occurs before 

 metakinesis (precocious division), and the two portions still remain con- 

 nected together by a portion of the original linin matrix or sheath, each 

 portion of a chromosome so produced has the value of only half a chromo- 

 some until it becomes separated from the other half in metakinesis, by the 

 rupture of the linin connection, when each half acquires the value of a 

 whole chromosome. The chromosome must be ascribed anactualvalue 

 (in relation to the cell generation in which it occurs) irrespective of 

 any prospective or retrospective value: its prospective or 

 retrospective valence does not modify its actual morphological valence, 

 for if it be assumed that it does (as is held by some), then the chromo- 

 somes of the spermatozoon or ovum, if we carry this assumption to 

 its logical conclusion, must have a valence nearly equal to infinity. 



This definition of the chromosome is the generally held idea of 

 the chromatin elements in the more normal (primitive) mitoses. Some 

 writers use chromosome in the same sense in the reduction divisions 

 also; but all writers do not, and this is how the discrepancy has 

 arisen in the terminology of the chromatin elements in the reduction 

 divisions. As long as it is assumed that the definition of the term 

 chromosome must remain purely arbitrary, no agreement can be reached 

 in the estimation of the value of these divisions. The definition given 

 by me above is not purely arbitrary: it is the accepted definition of 

 a chromosome in the more normal (primitive) mitoses, and to be logical 

 we are bound to use the term chromosome in the same way for the 



