A JVeiD Theory of Heredity. 95 



It is plain that if tlie cliuractor of important parts can 

 be thus changed by changes in other parts, the typical 

 or characteristic form of these parts may be due only 

 partially to heredity. 



We see then that the structural complexity of an adult 

 animal is due in part to the formation of structures 

 which are not alive, in part to the direct modifying in- 

 fluence of external conditions of life, and in j^art to the 

 action of one organ of the body upon another, so that 

 the number of features which are directly inherited is 

 very much less than the number which are constant in 

 and characteristic of the species. 



It is impossible for us to state at present how many 

 features must be subtracted from the race characteristics 

 of an animal in order to give us the total number of 

 hereditary cougenital characteristics. The observations 

 and experiments wliich are recorded are few in number, 

 but they are sufficient to show us that, in all the higher 

 animals, very considerable deduction must be made, 

 and we may be sure that the mature animal is vastly 

 more complex than the Q^g. There is still another lim- 

 iting circumstance which has not 3'et been mentioned. 



Many of the parts of an organism are due to in- 

 definite multiplication of a single element. The simplest 

 illustrations of this fact are the blood corpuscles of 

 vertebrates and the leaves of plants. It is clearly un- 

 necessary to suppose that each vertetrate ovum contains 

 separate particles for all the blood corpuscles, or that 

 each seed contains separate particles for all the leaves 

 which the plant is to produce. All that is necessary is 

 to assume that it contains particles which are capable 

 of producing a single one of these structures, with a 

 capacity for indefinite multiplication, and that surround- 

 ing conditions determine how far, and in what places, 



