The presentation of his idea in the form of the chain of 

 being is much closer, of course, to the evolutionary argument 

 in the spirit of Radishchev and Lamarck than to Bonnet's 

 metaphysical version. The graduation of structural complexity 

 which is recognized in a series of living creatures (from 

 infusoria to man) is, as Pavlov claimed, reflected in 

 embryonic development. "The formation and growth of the 

 fetus," he wrote, "represents a line which, beginning from 

 the lower animals and passing almost through all the steps 

 of the animal organism, reaches up to man" ($ 94). 



Pavlov suggested dividing the embryonic period into its 

 two stages: the stage of evolution or metamorphosis, during 

 which the development of the fetus is carried out, and the 

 stage of ripening or perfection, when the developing structures 

 reach maturity. Going back to the idea of the production in 

 ontogenesis of progressive levels of creation, he stated 

 that, so far as there is corresponding difference in the 

 structure of infusoria and mammals, their nutrition is also 

 different; is it not possible that during the first stage of 

 fetal development, when the organism becomes gradually more 

 perfect and complex, that nutrition has similarly become more 

 complex? The more complex the nutrition, the more perfect 

 the animal; hence the nutrition of the fetus during the first 

 developmental stage becomes more complex. 



With the second stage, when development ends, the type of 

 nutrition is stabilized. "In order to explain more properly 

 fetal nutrition from its beginning, comparative physiology 

 is recommended, beginning from simple creatures to the more 

 complex" (5 98) . "If you carefully trace the nature of 

 formation," Pavlov continued, "it is possible to see that body 

 rudiments originate in water. Crystals develop from the fluid; 

 the green material of Priestley is the beginning of plant life. 

 The infusoria, as the rudiments of animal life, also begin 

 with water" C$ 99) . "From here it is easy to understand why 

 the fluid condition represents a necessary condition for 

 the formation of all bodies" ($ 100) . Agreeing with the 

 physicists, Pavlov wrote that the fluid state of the body 

 undoubtedly precedes the solid state; thus the cellular 

 tissue itself, which is the basis of solid development in 

 the organism, initially develops from fluid. 



169 



