no POPULAR SCIENCE MONTHLY. 



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 there- 

 fore 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 in- 

 testine.* 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 : e 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 con- 

 siderations. 



But all Wolff's work was launched into an uncongenial atmos- 

 phere. 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. 



* ' De Formatione Intestinoram,' Nova Commentar, Ac. Sci. Petrop., St. 

 Petersburg, XII., 1768; XIII., 1769. > 



