144 PROCEEDINGS OF THE ACADEMY OF [March, 



of the forms to portions of the plant was discussed and the distribu- 

 tion of the species within the range of Covillea stated. Certain 

 other species of the order very commonly found on the same shrub 

 were afso mentioned. Specimens of the host plant of all the peculiar 

 species and a map of the distribution of the creosote bush were 

 exhibited. 



Henry Fairfield Osborn, D.Sc, LL.D. : "Tetraplasy, a Law of the 

 Four Inseparable Factors of Evolution."* 



Upwards of twelve years of work on the group of fossil mammals 

 first made known by Joseph Leidy, which may now be known popu- 

 larly as the Titanotheres, had led to the conviction that vertebrate 

 palaeontology may concern itself with two great questions in evolu- 

 tion: 



(1) The origin of new characters. 



(2) The transformation of existing characters. 



Excluding any external agencies, we must seek such origins and 

 transformations either in: 



(1) Environment, physical or biotic. 



(2) Ontogeny, that is, in the development of the body, or soma. 



(3) Heredity, or in the development of the germ. 



(4) Selection, or in the competition between organisms. 

 Having reached in 1905 the conclusion that our quest for the 



origin and transformation of characters must be directed to one or 

 the other of these four factors, working individually or separately, 

 the author published in 1908 what he believes to be the most funda- 

 mental biological law, and termed it The Law of the Four Inseparable 

 Factors.* 



In nature each of these factors is in aHsense independent, with its 

 peculiar or intrinsic phenomena; in another sense dependent, or 

 intimately related to each of the other factors. 



It is a striking fact in the history of biology, from the middle of 

 the 18th century, that the particular factor upon which naturalists 

 have concentrated their attention has seemed to them the all- 

 important or all-sufficient factor. Thus Environment in the minds 

 of Buffon, or Semper, or Wagner appeared to be the efficient cause 

 of evolution. Similarly, Ontogeny in the minds of Lamarck, Spencer, 

 Cope, seemed to be the primary source of evolutionary change. 

 Again, Selection in the minds of Darwin and Wallace, combined 

 with hereditary fortuitous variation, seemed to possess the chief 

 constructive power in evolution. Finally, as the latest phase, 

 Heredity, as developed by Galton, Weismann, Mendel, De Vries, 

 and Bateson, has come to be regarded as the chief centre of trans- 

 formation. 



4 " The Four Inseparable Factors of Evolution, Theory of their Distinct and 

 Combined Action in the Transformation of the Titanotheres, an Extinct Family 

 of Hoofed Animals in the Order Perissodactyla." Science, N. S., Vol. XXVII, 

 No. 682, Jan. 24, 190S, pp. 14S-150. 



