170 CHAKLES L. PARMENTER 



INTRODUCTION 



It is believed (McClung, '17, pp. 536-38) that the chromatin 

 of an organism is, for the most part at least, the idioplasm, and 

 consists of a definite linearly arranged series of differentiated 

 materials which is perpetuated from generation to generation. 

 The chromosomes which are essentially constant in number in 

 an individual are thought to constitute the visible mechanism 

 for this perpetuation. This conception is known as the theory 

 of the individuality of the chromosomes, which is quite generally 

 accepted by all who have an intimate acquaintance with chro- 

 mosome behavior. However, there are a few not so acquainted 

 who strenuously oppose the theory. 



Among these is Delia Valle ('09, '11, '12), who presents some 

 data and a large amount of discussion in an effort to disprove 

 this theory upon the claim that the chromosome number in an 

 individual is not constant, but is simply the quotient of the 

 quantity of chromatin divided by the average size of the chro- 

 mosomes. This removes from them any constancy of organiza- 

 tion and contradicts the above theory. These observations have 

 been cited by other opponents of the theory as cytological 

 evidence in favor of their contentions. Delia Valle's conclusions 

 are based upon observations made upon dividing cells of the 

 peritoneum and blood-cells of Salamandra maculosa, together 

 with a large amount of data taken from the observations of 

 others. 



Meves ('11) and Delia Valle ('12) further oppose the theory 

 upon the basis of linear measurements made upon the spermat- 

 ogonial and somatic chromosomes of Salamandra maculosa in 

 denying Montgomery's ('01) and Sutton's ('02) claim that the 

 chromosomes occur in pairs whose homologues are of equal 

 length, and that approximately constant size relations among 

 chromosomes are maintained from one cell generation to 

 another. 



In the spring of 1916 I was fortunate in obtaining peritoneal 

 and other somatic tissues of Ambystoma tigrinum. This made 

 it possible to repeat Delia Valle's observations upon the somatic 



