Page:Popular Science Monthly Volume 67.djvu/116

110 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 favorable to Malpighi. The latter shows much better, in corresponding stages, the series of cerebral vesicles and their relation 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 primitive kidneys, or 'Wolffian bodies,' of which he was the discoverer.

Although Wolff was able to show that development consists of a gradual formation of parts, his theory of development 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 the past was yet to be expressed. Wolff was therefore in the same quandary as his predecessors when he undertook to explain development. Since he assumed a total lack of organization in the beginning, he was obliged to make development 'miraculous' through the action on the egg of a hyperphysical agent. From a total lack of organization, he conceived of its being lifted to the highly organized product, through the action of a vis essentialis corporis

He returned to the problem of development later, and, in 1768-69, published his best work in this field on the development of the intestine. This is a very original and strong piece of observational work. While his observations for the 'Theoria Generationis' did not reach the level of Malpighi's those of the paper of 1768 surpassed it and held the position of the best piece of embryological work up to that of Pander and Von Baer. This work was so highly appreciated by Von Baer that he said: 'It is the greatest masterpiece of scientific observation which we possess' In it he clearly demonstrated that the development of the intestine, and its appendages, is a true process of becoming. Still later, in 1789, he published further theoretical considerations.

But all Wolff's work was launched into an uncongenial atmosphere. The great physiologist, Haller, could not accept the idea of epi genesis, but opposed it energetically, and, so great was his authority, that the ideas of Wolff gained no currency. This retarded progress in the science of animal development for more than a half century.

In 1812, the elder Meckel, recognizing the great value of Wolff's researches on the development of the intestine, rescued the work from neglect and obscurity, by publishing a German translation of the same, and bringing it to the attention of scholars. From that time onward Wolff's work began to be fruitful.