CHAPTER VII 



Experimental biology continued. The role of the chromosomes 

 in inheritance. Inheritance of sex and sex-linked char- 

 acters. 



In the preceding chapter we have considered the question 

 of the influence of the cytoplasm upon development, par- 

 ticularly in respect to the "organ-forming sub-tances" which 

 it contains; and the ability of one part of an organism to 

 regenerate, not only itself, but some other part normally 

 foreign to it. We shall now consider the role of the nucleus 

 in development, especially that of the chromosomes. 



Whether or not development be locally predetermined in 

 the egg, there is of course no question that the latter is pre- 

 determined in its general development. Men do not gather 

 "grapes of thorns or figs of thistles," nor can the specific, 

 e. g., characteristic of the species, development be altered by 

 any change in the environment. What is it then which deter- 

 mines the specific characters of the organism? 



While the theory of cellular units responsible for the 

 hereditary transmission of specific and individual characters, 

 originated with Darwin as the well known "pangenesis" 

 theory, in an attempt to explain the origin of new characters 

 by environmental influence, and was amplified and more 

 definitely formulated by Weismann, it has never received 

 stronger support than through the epoch-making work of Mor- 

 gan and his students at Columbia University within the last 

 decade. 1 



In order to appreciate the significance of this work, it is 

 necessary to turn back the pages of time for a half century 

 and pause a moment to look into the garden of the monastery 

 at Briinn in the Tyrol, where the monk Gregor Mendel was 

 busy with his peas. 



Mendel was monk and later abbot at Briinn, and for a time 



*I do not wish in this statement to accuse modern biologists of 

 accepting Darwin's theory of "pangenesis" in its entirety. Darwin- 

 ian and modern viewpoints have in common however the assumption 

 ol some sort of cell units, be they physical or be they chemical, which 

 are responsible for reappearance in the offspring of characters pres- 

 ent in the parent. 



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