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 te 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 pre-formation and encasement in his Theoria 
Gencralionis, 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 Wolfi’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 Wolfi’s observations. 
Wolff, on the other hand, figures for the first time the prim- 
itive kidneys, or ‘‘ Wolffian 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 
