OBSERVATIONS AND EXPERIMENTS 231 



acters and, at the same time, accounts for the great 

 variety of cases revealed by observation or experi- 

 mentation. Certain characters can be transmitted, 

 those, namely, which correspond to a substance pres- 

 ent, not only in the organ under consideration, but in 

 the ovum as well. They are not necessarily charac- 

 ters of prime importance, very noticeable or indis- 

 pensable to the life of the developed organism. They 

 are characters common to the organism and to the 

 ovum. 



Other characters, equally important perhaps, but 

 determined by substances which do not exist in the 

 ovum and only develop in the course of ontogenesis, 

 are not transmitted. The same holds true of mod- 

 ifications which, while very noticeable, bring about no 

 qualitative change in the composition of the blood. 

 This explains the contradictory results of the various 

 experiments bearing upon different somatic modifica- 

 tions. 



It is most natural that certain mutilations, such as 

 docked tails or amputated limbs, performed on organs 

 made up of tissues found everywhere in the organism, 

 should not be hereditary, as this occasions no qualita- 

 tive change in the blood. Things may be different, 

 however, when the organ resected contains the total- 

 ity of a certain kind of tissue. The organism is then 

 deprived of the substance characteristic of that tissue 

 and the sexual product, at the time of its formation, 



