ovum through many intermediate stages the final goal (ZEIL) 

 is reached— the fluttering butterfly. "20 "The more we enter 

 into details, the more completely this special relation 

 (ZWECKBEZIEHUNG) appears. It must be noted that for the 

 work which must be performed in each separate condition, all 

 necessary instruments are not only present at the necessary 

 time, but are formed in the previous condition. "21 



"Themaxillae and extremities of the caterpillar, which 

 are adapted to its form of life, are developed in the ovum, 

 so that from the moment of hatching everything necessary for 

 the function of intensive feeding is already prepared. The 

 organs of the butterfly— wings, long legs and spiral proboscis 

 — are developed in the pupa stage, i.e. long before these 

 organs will be used. Within the hard shell of the pupa, 

 internal transformations take place which are completely 

 connected with the future and not with the present. "22 



Baer also discussed this question in detail in the 

 second article, considering the continuation of the work 

 "On Purpose in the Phenomena of Nature" and entitled "On the 

 Trend of Processes, Especially in Organic Bodies. "23 



Speaking of embryonic development, he noted that already 

 in the earliest stages the material of the ovum is processed 

 for the formation of organs, so that development proceeds 

 "as if there sits in the ovum a judicious and understanding 

 builder. "24 This metaphor was necessary to underline that 

 from his point of view the vital process in particular' and 

 the development of the individual is characterized by a trend 

 towards a definite end, although the ovum and the developed 

 embryos, of course, do not recognize this end. Here Baer 

 also had mentioned that the trend of development is not 

 absolute, but adapted to surrounding conditions; thus, the 

 eggs of birds require the effect of heat and the free flow 

 of air. The necessity for determined conditions for develop- 

 ment is shown also by other animals; their life, i.e. 



20. Ibid ., p. 54. 



21. Ibid ., p. 55. 



22. Ibid., g. 53. 



23. Baer, "Uber Zielstrebigkeit. " 



24. Ibid ., p. 228. 



498 



