in the discussed work. Already in the beginning of the work 

 ($ 2), Wolff confirmed that he could understand the initial 

 stages of the genesis of the intestinal canal only because 

 he traced the entire process of development of the intestine 

 from the moment of its formation to its final completion. 

 Wolff expressed a hope that his theory about formation of 

 the intestinal canal would be acceptable for experienced 

 naturalists, as it is nearly wholly taken from observations. 



In another place (5 81) Wolff described his method of 

 studying the developing eggs, which he considered the only 

 suitable method, in order to make the description of the 

 phenomena completely understandable; thus: "I selected the 

 following order in the description of the phenomena in the 

 incubated egg. From the beginning I described the phenomena 

 at that time when they attain the highest development.... 

 then I followed them to the moment of appearance, described 

 the changes which occur from their first appearance to that 

 time when their essence can be determined. Finally I explained 

 the other changes, which occur in the period up to the full 

 completion of the process." 



Passing to the statement of the basic results of his work, 

 Wolff turned attention to the previously insufficiently studied 

 membranes which already surround the embryo in the first days. 

 He gave the study of the membranes special significance because 

 according to his data the intestinal canal originates from 

 these peculiarly structured membranes. 



From the subsequent text it is clear, without doubt, 

 that Wolff still could not differentiate the true preliminary 

 membranes (serosa and amnion) , formed from the extra-embryonic 

 parts of the ectoderm and mesoderm, from the embryonic layers, 

 from which the embryo itself developed. According to his 

 description, the condition of the egg about the middle of the 

 third day of incubation is seen in Figure 6. A part of the 

 yolk membrane, as Wolff called it, very rich in vessels, and 

 the center of which is called the vascular area (area vasculosa) 

 is where the embryo is found. This part is composed of two 

 layers; the external layer is delicate, transparent and is 

 deprived of vessels. It goes above the embryo and is loosely 

 united with the internal layer so that during immersion in 

 water it separates from it and comes to the surface. And the 



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