HEREDITY. 445 



Osborn points out that Euffon appealed to the 

 "direct action of the environment" as a cause of evo- 

 lution, in so general a way, as to embrace all the con- 

 ditions above enumerated. St. Hilaire dwelt on the 

 embryogenic influences, while Lamarck laid stress on 

 the somatogenic. Darwin only discussed variation 

 after it came into being. 



The distinctions pointed out by Osborn relate to 

 the period of life at which modifying influences are 

 experienced ; that is, they are time distinctions. They 

 must all, however, be included under two heads when 

 the sources of influence are considered. That is, they 

 must proceed from the organism itself, or from the en- 

 vironment directly. Those proceeding from the or- 

 ganism may also be divided into two classes, viz., 

 those which are inherent in the physical and chemical 

 characters of protoplasm, and those which have been 

 acquired by generations prior to any given one under 

 consideration. In this work I attend first to the prob- 

 ably efficient or phylogenetic causes, and these may be 

 regarded as having been at some time or another dur- 

 ing the history of the phylum as somatogenic. On 

 this view, I have regarded the life of an animal as 

 divided into three periods ; those of embryonic life, of 

 adolescence, and of maturity. During embryonic life 

 impressions are exclusively somatic, and can be only 

 obtained through or from parental stimulus and parental 

 environment. Such will reach the embryo through nu- 

 trition, and through the direct mechanical contacts and 

 strains of the environment. The environment of unpro- 

 tected embryos is external to the parent ; that of long 

 protected embryos is the walls of the oviduct, uterus, 

 etc., within the parent. Ryder has alleged with much 

 reason that the nature of the contact of the chorion with 



