Repeatedly, it was noticed that Wolff pioneered the idea of 

 unity of the morphological structure of plants, brought 

 together to a general form in the leaf, which was later 

 worked out in detail by Goethe. This side of Wolff's scien- 

 tific interests is indirectly related to the basic direction 

 of his activity. 



Passing to the morphology of animals, Wolff noticed that 

 the analogy cannot be established between the individual parts 

 which exist in plants, and the different organs which exist 

 in the animal body. The organized body of the animal is a 

 very complicated whole; it originates as a result of inter- 

 action of many interconnected dependent causes. One of the 

 forms of development characteristic for animals is similar to 

 the development of plants; it appears in the formation of the 

 extremities. Wolff wrote the following: 



The extremities, i.e. wings and legs of birds, first 

 appear in the form of protuberances , and then 

 elongate; at their ends new protuberances appear 

 which are the rudiments of the fingers, and gradually 

 they acquire the form and structure of the formed leg 

 and wing. Something similar occurs in vegetation, 

 as the leaves of plants are formed; this common mode 

 of formation I stated in the theory of generation. 3 



This process of development is realized when, at the 

 beginning, the nutritional fluid collects in the already 

 existing parts and causes a protuberance to appear, which is 

 the first rudiment of a new part. This fluid is gradually 

 transformed into a more compact substance. Simultaneously 

 with this, vessels appear in it, through which new nutritional 

 juices flow. By this means a new part is organized, i.e. 

 acquires structure. Similarly new protuberances appear in 

 different places, being the rudiments of new parts. 



In animals, other types of generation and development 

 of parts of the body also exist. Thus, a different type of 

 development than that just described characterizes the 

 intestine, the fundamental object of Wolff's observations 



2. DE FORMATIONE, p. 410. 



3. Ibid., pp. 411 - 412. 



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