AND ITS SELF-CONSERVATION". 277 



known to swerve from the pattern of the parent animal 

 that gave it birth"* only, the "pattern" is nothing 

 more nor less than that general, unchangeable type 

 within which the individual nay, countless genera- 

 tions of individuals may and must vary in their ceaseless 

 struggle for that degree of existence in which the type 

 is most fully realized. Doubtless no egg that owes 

 its parentage to a vertebrate can ever develop into any 

 other than a vertebrate animal. But this does not in the 

 least invalidate the conception that while in one locality 

 of the primitive world the eggs of the primal vertebrate 

 were developing in the direction of the fish, in another 

 locality where the conditions were different the eggs of 

 the primal vertebrate were developing in the direction of 

 the mammal. Thus proceeded, as it would seem, the 

 differentiation of the primal "generalized" (that is, as 

 yet for the earth unspecialized) type of vertebrate animals; 

 and always it proceeded in accordance with, as. the pro- 

 gressive realization of, the perfect plan, the unalterable 

 method, by which the divine World-Energy is forever 

 unfolding itself in Creation as a whole. 



It may very well be that there are "sundry traits in 

 common," as between certain molluscoid animals and the 

 lowest vertebrate animal, f *But this is only to say that 

 the nearer we approach the beginning point in the 

 development of animal forms on the earth, the more 

 manifest is the homogeneity characterizing those forms. 

 In other words, it simply indicates their common origin 

 in an undifferentiated animal unit already developing in 

 myriad duplications in the primal sea. 



* "Methods of Study in Natural History,'' 1 p. 29. 



t Herbert Spencer: "Principles of Biology," II., 567. 



