246 THE ORIGIN AND EVOLUTION OF LIFE 



tionswediscls), first clearly enunciated by Anton Dohrn in 1875. 

 But no function is lost without good cause, and the heredity- 

 chromatin retains every character which through change of 

 function and adaptation can be made useful. 



The same law which we observe in the conservation of all 

 adaptive characters and functions will probably be discovered 

 also in the conservation of ancestral physicochemical actions, 

 reactions, and interactions of the organism from the protozoan 

 stages onward. The primordial chemical messengers — enzymes 

 or organic catalyzers, hormones and chalones, and other accele- 

 rators, retarders, and balancers of organ formation (see p. 72) — 

 are certainly not lost; if useful, they are retained, built up, and 

 unceasingly complicated to control the marvellous coordina- 

 tions and correlations of the various organs of the mammalian 

 body. The principal endocrine (internal secretory) as well as 

 duct secretory glands established in the fish stage of evolution 

 (p. 160), through which they can be partly traced back even to the 

 lancelet stage (chordate), doubtless had their beginnings among 

 the ancestors (protochordates) of the vertebrated animals, which 

 extend back into Cambrian and pre-Cambrian time. Since 

 these chemical messenger functions among the mammals are 

 enormously ancient, we may attribute an equal antiquity to the 

 powers of chemical storage and entertain the idea that the 

 chromatin potentiality of storing phosphate and carbonate of 

 lime for skeletal and defensive armature in the protozoan 

 stage of 50,000,000 years' antiquity is the same chromatin 

 potentiality which builds up the superb internal skeletal struc- 

 tures of the Mammalia and the highly varied forms of offen- 

 sive and defensive armature either of the calcium compound 

 or the chitinous type. 



It is, moreover, through the fundamental similarity of the 

 physicochemical constitution of the fishes, amphibians, reptiles, 



