continuous internal preformation, can take place only during 

 suitable external conditions. "Life," Baer wrote, "is nothing 

 other than a movement towards a definite final self- 

 transformation, adapted to external conditions." To illustrate, 

 Baer described the early stages of development of the eggs of 

 the hen, of the frog, and of the sea urchin, and also 

 described the behavior connected with reproduction. 



From the actual data cited, he concluded the following. 

 The physico-chemical processes in the early stages of develop- 

 ment, when their direction appears, have been studied very 

 insufficiently. In the vertebrate embryo, two shafts ascend 

 on the dorsal side which are then united in a tube; the 

 results and the significance of this process is clear: the 

 central nervous system is formed from the internal layer of 

 the tube, and from the external layer the bones, muscles, 

 and skin are formed. "Thus, in relation to this process, 

 the question why is very easy to answer, and the question, 

 by what means does it happen, remains completely open for 

 the naturalist. Naturally, one doubts that this process is 

 conditioned by physical necessity, since the end of any 

 process is reached only on the basis of the laws of nature; 

 without reference to the latter, any phenomenon must be 

 considered magic. "25 



"I can then repeat the question," Baer continued, "how 

 is it possible to overemphasize that all these processes 

 are related to future requirements? They are directed to 

 what must originate. Philosophers who wrote in Latin called 

 this relation causa finalis , or final cause (ZIEL) .... 

 And in all other animals the changes following one after 

 another must serve a purpose (ZWECKSINNLICH SEIN)." 26 

 For the exact understanding of Baer's idea it is necessary 

 to review his terminology. In the German language there are 

 two words — ZWECK and ZIEL — which are both translated into 

 the Russian language as "purpose"; as a matter of fact, in 

 the normal German usage as well, these words can replace each 

 other. However, Baer found in them this shade of meaning; 

 he considered it possible to use them for the designation of 

 different concepts, proceeding from the following considerations 



25. Ibid ., £. 192. 



26. Baer, "Uber den Zweck," p. 51 



499 



