104 



THE AMERICAN NATURALIST 



[Vol. LVI 



Of course, it is not difficult to imagine a sufficiently 

 close approach to continuity of evolution, and therefore, 

 to orthogenesis, in the case of simple proteins. But 

 here, very likely on account of our ignorance, there is no 

 indication of anything more than indefinite variation and 

 variability, accompanying variation in a definite direction 

 in the morphological characteristics of species. 



On the whole, variation in the ultimate physico-chem- 

 ical nature of organisms seems to have been rather dis- 

 crete than continuous, not orthogenetic, but distributed 

 at random. Such a conclusion may possibly be illusory, 

 for our ignorance is greater than our knowledge. But 

 whatever the nature of the changes which it has under- 

 gone, the most striking thing about the physico-chemical 

 nature of protoplasm seems to be its uniformity through- 

 out nature. 



Therefore, with due reservations because of the incom- 

 pleteness of bio-chemical knowledge, it seems reasonable 

 to suppose that apparent instances of orthogenesis may 

 sometimes depend upon a single important chemical 

 change in an organism, followed by slow and progressive 

 modifications leading up to a definitive morphological re- 

 sult. Such a process would be somewhat analogous to 

 the establishment of a condition of equilibrium. 



