INTRO D UC TION. 7 



place at points where the tension is excessive." Quite 

 as specific is iiis ascription of the forms of epithelial 

 cells to definite causes, as follows:^ " Just the equal- 

 ities and inequalities of dimensions among aggregated 

 cells, are here caused by the equalities and inequalities 

 among their mutual pressures in different directions ; 

 so though less manifestly, the equalities and inequali- 

 ties of dimensions among other aggregated cells, are 

 caused by the equalities and inequalities of the osmatic, 

 chemical, thermal, and other forces besides the me- 

 chanical, to which their different positions subject 

 them." 



In spite of this not infrequent definiteness, Mr. 

 Spencer occasionally falls into the error of ascribing 

 the origin of structures to natural selection, as in the 

 case of the forms of flowers,- and the armor-plates of 

 paleozoic fishes.^ Spencer assumes the inheritance of 

 acquired characters throughout. 



In 1866 Haeckel's SchopfungsgcscJiicJitc appeared. 

 In this work the author presents a mass of evidence 

 which sustains the doctrine of evolution, and he com- 

 bines the views of Lamarck and Darwin into a general 

 system. He says :^ "We should, on account of the 

 grand proofs just enumerated, have to adopt Lamarck's 

 theory of descent for the explanation of biological phe- 

 nomena, even if we did not possess Darwin's theory of 

 selection. The one is so completely and directly proved 

 by the other, and established by mechanical causes, 

 that there remains nothing to be desired. The laws 

 of inheritance and adaptation are universally acknowl- 



1 op. cit., p. 260. 



2 op. cit., p. 153. 



3 0/. cit., p. 288. 



^Thc History of Creation, Amer. Edition, II., p. 355. 



