70 BULLETIN OF THE 



shall develop than the pabulum, or environment, or alf the mighty 

 chemical and physical forces that are brought into play as the pro- 

 cess goes on. In a word, the individual developes after the pattern 

 of its parent, or not even all the solar energy can compel it to 

 develop it at all. 



We are thus brought face to face with the facts of sexual gener- 

 ation, and especially of heredity, with all their wide bearings on 

 the great biological questions of natural selection and the origin of 

 species. Into the details of these large questions the limits of the 

 hour will not permit me to enter. Could I take time to do so, I am 

 satisfied that at every step I should be able to collect for you ad- 

 ditional evidence of the existence of a vital principle. Still I 

 regret this the less because most of you, I think, are so familiar 

 with the modern literature of these subjects, and especially with 

 the admirable writings of Mr. Darwin, that I feel sure, if I can suc- 

 ceed in giving you a clear outline of my views, much that I should 

 say, had I time, will suggest itself to your own minds. In a gen- 

 eral way, however, when we study, in the history of life upon this 

 globe, the double phenomena of long continued persistence of type, 

 and of slow variation continually occurring, we will find that almost 

 all biologists, whatever their theory of life, explain these phenomena 

 on the one hand by heredity, on the other by the sensibility of the 

 organism to the influence of the environment. 



Both heredity and the influence of the environment may be very 

 conveniently studied in those simplest organisms in which each in- 

 dividual consists of a single minute mass of naked protoplasm, as 

 in certain rhizopods, for example, the amoeba. These tiny creatures 

 produce a progeny which preserves the parental type as closely as 

 is done by the offspring of the higher animals. Their sensibility to 

 the influence of the environment is manifested in several ways. 

 They grow, that is they appropriate materials from the environ- 

 ment, in the way I have already specified ; they manifest automatic 

 movements, that is, on encountering food, obstacles, or other dis- 

 turbing external circumstances, movements result the direction and 

 energy of which are in no wise determined by the character or 

 force of the external influences, or as they may be conveniently 

 termed the stimuli by which these movements are provoked ; and 

 finally, simultaneously with the process of growth, a certain meta- 

 morphosis, or metabolism, of the protoplasm is continually going on 

 resulting in the formation of excrementitious substances which are 

 continually being excreted. 



