The Process of Heredity 55 1 



V DISCUSSION 



TJie Relative In-fluence of Maternal and Paternal Elements in 

 Determining the Characters Seen in Early Development 



Driesch/ as the result of his hybrid experiments with various 

 species of echinoids, came to the conclusion that the early develop- 

 ment of hybrids is practically determined by the character of 

 the egg protoplasm; that the rate of cleavage, the number of pri- 

 mary mesenchyme cells, the form of the larval body, and the color 

 content of the hybrid tissues, are exclusively maternal characters, 

 and that no male influence is felt until a comparatively late period, 

 when the larval skeleton is forming. These rather sweeping con- 

 clusions were subsequently modified to a slight extent in response 

 to a criticism by Boveri.^ Driesch^ admitted that at least one of the 

 characters claimed by him to be pure maternal, showed the male 

 influence. This was the character of intensity of coloration of the 

 hybrid larvae. Further than that he was unwilling to go. 



Boveri showed that the number of mesenchyme cells is notice- 

 ably influenced by the male parent. In fact, it appears from 

 Boveri's work that the form of larval body and almost every char- 

 acter of the hybrids show the paternal influence. It was admitted, 

 however, that the chief controlling factor in early development is 

 the egg protoplasm. 



Driesch and Boveri have never reached an entire agreement on 

 this matter. They stand for two opposite doctrines of heredity. 

 Boveri is a stanch champion of the idea that the nucleus is the 

 sole bearer of hereditary material and hence has a tendency to 

 overemphasize the paternal influence, since he believes the sperm 

 cell to consist almost entirely of nucleus. Driesch, on the other 

 hand, believes firmly that the cytoplasm is of equal value in inherit- 

 ance, and somewhat oversteps the mark in claiming that the egg 

 protoplasm is the sole factor in determining the character of the 

 phenomena of early development. 



The data advanced in the present paper lead to a middle course. 

 For merely mechanical reasons the egg protoplasm must necessarily 



^ Driesch, H. Arch. f. Entw.-Mech., 7, 1898. 

 ^Boveri, Th. Arch. f. Entw.-Mech., 16, 1903. 

 * Driesch, H. Arch. f. Entw.-Mech., 16, 1903. 



