H33 



students of the subject, quite different schemes of cell divisions have 

 been proposed. According to Brauer's observations on Ascaris , the 

 chromosomes undergo two successive longitudinal divisions during 

 maturation. Henking, who investigated the maturation divisions of a 

 number of species of insects, concluded that the first division is trans- 

 verse and the second longitudinal. My own observations upon the 

 maturation process as occurring in insects and mammals, including 

 man, led me to deny the existence of any longitudinal division during 

 maturation, in the sense in which that term is ordinarily used. 



It is apparent, therefore, that all the possibilities have been ex- 

 hausted with reference to the kind of divisions which may occur during 

 maturation and the order of their succession. The chief question 

 which it is my purpose to discuss here grows naturally out of this 

 state of affairs. This question is whether the longitudinal division of 

 a chromosome can reasonably be assumed to be essentially different 

 from a transverse division. As first interpreted by Weismann and 

 according to the phraseology of nearly all later writers on the subject, 

 a longitudinal division of a chromosome has been assumed to produce 

 two chromosomes which are qualitatively and quantitatively identical ; 

 while a transverse division is said to produce two chromosomes which 

 are quantitatively equal but qualitatively unlike. So far as known 

 to the writer no one has ever questioned the validity of this arbitrary 

 distinction. When, however, the origin of chromatic elements from 

 minute and scattered chromatic particles is considered, it seems strange 

 that any one would assume that a longitudinal division would give 

 results essentially different from those of a transverse division. The 

 statement has been repeated in the literature of the subject times 

 without number, that in a longitudinal division all of the elements of 

 heredity which constitute a chromosome are exactly halved, so that 

 each daughter chromosome receives one-half of all possible ancestral 

 tendencies, and is therefore exactly identical with the other. 



All investigators of this subject admit that previous to the first 

 maturation division the chromosomes are broken up into an immense 

 number of minute particles, some of which are assumed to be too 

 small for definition by the microscope and the material of which is 

 even described as being in a sort of solution. Chromosomes wich 

 succeed upon this stage are formed by the gradual association and 

 condensation of these minute particles. A chromosome, therefore, 

 must be considered as made up of an indefinite number of minute 

 particles of chromatic matter, which have arisen by gradual couden- 



