THE SPEEMATOZOON. 19 



conclusion that the particles of the chromatic substance are the bearers of 

 hereditary tendencies and capabilities. 1 If this is the case, then they are the 

 means by which ancestral possessions, in the morphological sense, are transmitted 

 from generation to generation. There is evidence also, first ascertained by Mendel 

 and substantiated and increased in recent years by his followers, which lends 

 probability to the belief that the tendency carriers form two main groups : (1) 

 those which carry certain tendencies ; (2) those which carry opposite tendencies. 

 The bearers of tendencies and the bearers of their opposites are allelomorphic 

 or alternative to each other, and are called allelomorphs. Thus the particles 

 which bear tallness and dwarfness respectively are allelomorphs, that is, they are 

 alternative to each other. 



Further, the facts which are known suggest the idea that in the primitive gerrn 

 cells, and their descendants which contain the typical number of chromosomes, the 

 character-bearing particles are arranged in pairs of which both elements may bear 

 the same tendencies, or one may bear one tendency and the other the opposite. 



For example, if red and blue be supposed to be opposite tendencies carried by 

 different particles or allelomorphs, then the germ cells of any given animal, male 

 or female, may contain either a pair of red-bearing particles, a pair of blue-bearing 

 particles, or a red and a blue bearing particle associated together as a pair. 



The reduction of the chromosomes during the maturation divisions of the germ 

 cells is an admitted fact, and it is believed that the reduction is a necessary 

 preliminary to the union of a male and a female gamete to form a zygote from 

 which a new individual may arise. It is assumed that the purpose of the 

 reduction is the segregation of the different tendency bearers from each other 

 in order that they may enter into new combinations. If this assumption is 

 correct, then every mature germ element or gamete contains only one element of 

 any given pair of tendency bearers, in the supposititious case under consideration, 

 either the red or the blue bearer, but not both ; and the object of the reducing 

 division is the segregation of the allelomorphs in order that they may enter into 

 new and possibly into different combinations, producing new and possibly varied 

 results. 



If, in the case of any given group of animals, the mature germ cells of some of 

 both sexes contain the blue-bearing particles and others the red-bearing particles, 

 it necessarily follows that three possible results may ensue when impregnation 

 occurs, that is when two mature germ cells unite to form a zygote. 



(1) A female gamete bearing red tendency particles may fuse with a male 

 gamete bearing red tendency particles ; (2) a female gamete bearing blue tendency 

 particles may meet and fuse with a male gamete bearing blue tendency particles ; 

 (3) a female gamete bearing red tendency particles may meet and fuse with a male 

 gamete bearing blue tendency particles. The constitution of the zygotes formed 

 may be stated as follows : 



EK BB EB, 



and the character of the individual developed from the zygote will vary according 

 to the combination. If two red tendency bearing gametes meet, the individual 

 will be red ; if two blue tendency bearing gametes meet, the individual produced 

 will be blue ; but when a gamete bearing red tendency particles unites with a 

 gamete bearing blue tendency particles the individual will be either red or blue 

 or a combination of the two, the result depending upon the relative potency or 

 dominance of the two tendencies. 



Further exposition of this interesting subject would be out of place in a text- 

 book of anatomy, but it is of such great importance in association with the trans- 

 mission of hereditary characteristics and hereditary diseases that every medical 

 student should make himself familiar with its possibilities by consulting the works 

 of Bateson, Punnet, and other writers and observers who are attempting to solve 

 the complicated problems which it presents. 



1 It must be understood that this function, if it exists, does not prevent the chromatic particles possessing 

 other functions, and that there is no evidence that the potency of a tendency depends upon amount of chro- 

 matic substance. 



