210 BIOLOGY AND ITS MAKERS 



ceived of by him as a necessity, when the last germ of this 

 wonderful series had been unfolded. 



His successors, in efforts to compute the number of 

 homunculi which must have been condensed in the ovary of 

 Eve, arrived at the amazing result of two hundred millions. 



Work of Wolff. Friedrich Kaspar Wolff, as a young 

 man of twenty -six years, set himself against this grotesque 

 doctrine of prc-formation and encasement in his Theoria 

 Generation-is, published in 1759. This consists of three 

 parts: one devoted to the development of plants, one to the 

 development of animals, and one to theoretical considera- 

 tions. He contended that the organs of animals make their 

 appearance gradually, and that he could actually follow their 

 successive stages of formation. 



The figures in it illustrating the development of the chick, 

 some of which are shown in Fig. 63, are not, on the whole, 

 so good as Malpighi's. Wolff gives, in all, seventeen figures, 

 while Malpighi published eighty-six, and his twenty figures 

 on the development of the heart are more detailed than any 

 of Wolff's. When the figures represent similar stages of 

 development, a comparison of the two men's work is favor- 

 able to Malpighi. The latter shows much better, in corre- 

 sponding stages, the series of cerebral vesicles and their rela- 

 tion to the optic vesicles. Moreover, in the wider range of 

 his work, he shows many things such as the formation of 

 the neural groove, etc. not included in Wolff's observations. 

 Wolff, on the other hand, figures for the first time the prim- 

 itive kidneys, or "Wolfnan bodies," of which he was the 

 discoverer. 



Although Wolff was able to show that development con- 

 sists of a gradual formation of parts, his theory of develop- 

 ment was entirely mystical and unsatisfactory. The fruitful 

 idea of germinal continuity had not yet emerged, and the 

 thought that the egg has inherited an organization from 



