viii PREFACE. 



listed by McCalla & Stavely the same year. Read before the American 

 Association for the Advancement of Science, at Detroit, August 27, 1871. 

 Received the Walker prize of the Boston Society of Natural History. 

 In this essay were added to the preceding, the following hypotheses: 

 . 1. The law of repetitive addition, in which the structures of animals 

 were shown to have originated from simple repetitions of identical ele- 

 ments. 



2. The existence of an especial force which exhibits itself in the growth 

 of organic beings, which was called growth-force, or bathmism, 



3. That development consists in the location of this energy at certain 

 parts of the organism. 



4. That this location was accomplished by use or effort, modifying and 

 being modified by the environment; or the doctrine of kinetogenesis. 



5. That the location of this energy at one point causes its abstraction 

 from other points, producing "complementary diminution" of force at the 

 latter. 



6. That the location of this energy, so as to produce the progressive 

 change called evolution, is due to an influence called " grade influence." 



7. That inheritance is a transmission of this form of energy, which builds 

 in precise accord with the sources from which it is derived. 



8. That this " grade influence " is an expression of the intelligence of 

 the animal, which adapts the possessor to the environment by an " intel- 

 ligent selection." 



9. An attempt to account for the origin" of " mimetic analogy " by 

 "maternal impressions." 



On these propositions, the following comments may be made : First, 

 the law of repetitive addition is much like the law of rhythm previously pro- 

 posed by Herbert Spencer.* Second, the force of growth, or bathmism, 

 had already been called constructive force by Carpenter, who, however, 

 did not treat of its evolutionary or " grade " characteristics. That such 

 force exists there can be no doubt at the present time, but it may be that 

 its varied aspects should each be considered a separate species of force (i. e., 

 energy). Third, the relations of the energetic and static conditions of this 

 force were considered, but were not sufficiently followed out to be clear. 

 It is hoped that greater clearness has been attained by the omission of 

 a few paragraphs and the insertion of an explanatory foot-note. 



Fourth, that the location of this energy is due to the influence of use 

 and effort. The doctrine of the development of parts of living beings by 

 use, and their loss by disuse, is well known to have been put forth by 

 Lamarck in 1809, who devotes one of the longest chapters (No. VII) of his 

 " Philosophic Zoologique " to its discussion. He did not, however, include 

 the element of efort, prior to the appearance of any rudiment of an organ, 

 in his hypothesis, which was proposed, so far as I know, for the first time 

 in the present essay. The doctrine of use and disuse has been sustained 



* « 



Principles of Biology.'* 



