Wolff began his description of kidney development 

 with demonstrations that up to the fourth and fifth days 

 of incubation the embryos are deprived of any trace of the 

 kidney. Only at this stage their first rudiments appear in 

 the form of accumulated cellular tissue in the area of the 

 lumbar vertebrae, joining the vertebral column from the front 

 (Fig. 3, 13). From these rudiments, oval bodies of the 

 kidneys are later formed. The ureters develop from their 

 posterior end leading into the rectum (Figs. 3, 17, 

 § 220 - 221) . Since Wolff made the first description of 

 kidney development, the kidney in this stage of formation, 

 or mesonephros, received the name Wolffian body. Wolff 

 emphasized that the substance from which the organs form 

 contains nothing except the slightly formed globules (§ 230) . 



From the first two parts of Wolff's dissertation, which 

 are almost without polemical discussions, it is clear that 

 his task was to demonstrate with factual data how the 

 development of plant and animal organisms is accomplished. 

 Each of the examples he mentioned show satisfactorily that 

 there is no pre-existence or preformation, and that the parts 

 of the developed organism are formed anew from structureless 

 material. To summarize: The first step is the formation of 

 vesicles or globules which, through nutrition, increase in 

 number and in this way form cellular tissues, the material 

 for building organs. The generalization that these globules 

 are the basis for both the rudiments of organs and the 

 actual organs in both plants and animals holds paramount 

 importance. It represents the basic doctrine about the 

 composition of all the organic bodies from cells, i.e. 

 the cell theory, which was formulated only eighty years 

 later. Wolff's significance as one of the early contributors 

 to the cellular theory has been repeatedly presented in 

 literature' and need not be discussed here in further detail. 



The third part of Wolff's German THEORIE , titled "On 

 the organic bodies of nature and on their development 



See, for example, Z[akharie) S(aulovich) Katsnel'son, 

 STO LET UCHENIYA KLETKE . ISTORIYA KLETOCHNOI 

 TEORII (Hundred years study about the cell. History of the 

 cellular theory) , Moscow: Akademii Nauk , 1939, and 

 B. E. Raikov, pp. 54, 64 - 65. A. E. Gassinovich in the 

 above-cited article about Wolff rightly warns against the 

 categorical confirmation of Wolff's role in the substantia- 

 tion of the cellular theory. 



61 



