object of Wolff's investigation was the development of the 

 chick embryo in the first stages of incubation. As in plants 

 and in animals, the cause of development, according to Wolff, 

 is the essential power and the ability of solidification of 

 the living substance. 



Wolff noticed in the 28-hour embryo a characteristic 

 external form and position of the yolk. Concerning the 

 internal structure, he found at this stage only the presence 

 of globules scarcely connected with each other; the embryo 

 was transparent and of semifluid consistency. It was impossible 

 to differentiate either heart, vessels or red blood in it 

 ($ 166). In the commentary to this paragraph Wolff dwelled 

 on the fundamental argument of preformationists, who 

 explained the invisibility of the preexisting structures by 

 the insufficiency of their optical means, and also by the 

 characteristics of the embryo itself, beginning with its 

 transparency. First of all he took notice of the accusation 

 he anticipated from his scientific opponents, and admitted 

 that it is impossible to consider non-existing that which 

 is beyond direct perception. That is why he also had 

 mentioned that this principle has a character of sophism 

 rather than truth. Since the particles from which all early 

 rudiments of animal organs originate are globules visible 

 by average magnification of the microscope, then it is 

 impossible to say that the parts of the body of the embryo, 

 if they are preformed, are beyond perception. "Thus," Wolff 

 wrote, "the confirmation that the parts of the body of the 

 embryo are latent due to their infinitely small size, and that 

 they only become visible gradually later on is considered a 

 fable." Continuing, he noticed that it is accurate to explain 

 the way nature produces the parts of the organism, 

 particularly in the formation of the extremities (5 217 

 and following), kidney ($ 220 and following), and so on. 

 The transparency, which truly disturbs observation, he did not 

 consider insurmountable. The body looks transparent in 

 this case if it lies on another body, in it or under it. 

 If the transparent formation is placed so that it will not 

 be connected with other parts, then it cannot escape observa- 

 tion. 



Undoubtedly, Wolff's claim that even "with the help of 

 stronger lenses no one discovered those parts which are not 



53 



