Weismanns Theory regarding the Constitution of Germ 

 Plasm. — "The physical basis of inheritance — ^the germ 

 plasm— Ues in the chromatin of the nucleus of the germ cell, 

 which takes the form of a definite number of chromosomes 

 or idants. 



"The chromosomes consist of ids, each of which con- 

 tains a complete inheritance. 



" Each id consists of numerous primary constituents or 

 determinants. 



"A determinant is usually a group of biophors, the 

 minutest vital units. 



'The biophor is an integrate of numerous chemical 

 molecules (Compare with Morgan's views). 



Chapter 10— CONGENITAL AND ACQUIRED 



CHARACTERS 



Two facts stand out prominently in the study of suc- 

 cessive generations of individuals in both plants and ani- 

 mals : 



(1) The strong resemblance or the persistence of like 

 characters from generation to generation, the idea being 

 often expressed by the phrase "like begets like;" and 



(2) the occurrence of variations among individuals 

 even of the same parentage, expressed by the phrase "like 

 begets unlike." 



These conclusions hold true whether the plant or ani- 

 mal is produced asexually'or sexually. There are, it is true, 

 differences among organisms in degree of variability, but 

 the fact of universal variability remains. 



In the discussion of characters that may be transmitted 

 two kinds are generally recognized, viz.: congenital, or more 

 correctly blastogenic. i.e., those characters "that have aris- 

 en through causes affecting the germ plasm directly; and 

 acquired or somatogenic, those that affect the body during its 

 development.' It is conceded that congenital or blastogenic 

 characters can be and are transmitted, but it has long been 

 disputed whether acquired or somatogenic characters can be 

 transmitted (Neo-Darwinian and Neo-Lamarckian discuss- 

 ions). In other words, it is not conceded that "structural 

 changes in the body induced by changes in functional or en- 

 vironmental influence will specifically affect the reproduc- 

 tive cells; that these will, if they develop, reproduce the 

 modification acquired by the parent or parents." 



The weight of evidence seems to be against the theory 

 of transmission of acquired characters. 



57 



