Chap. III. EMBRYOLOGICAL SYSTEMS. 221 



supported by such an extensive acquaintance with the subject, as this great embry- 

 ologist has in his " Scholicn und CoraUarien zu der Entwickehmgsgeschichte des 

 IlUhnchens im Eie." ^ These principles are presented in the fonn of general pro- 

 portions, rather than in the shape of a diagram with definite systematic names, and 

 this may explain the neglect which it has experienced on the part of those who 

 are better satisfied with words than with thoughts. A few abstracts, however, 

 may show how richly the perusal of his work is likely to reward the reader. 



The results at which K. E. von Bacr had arrived by his embryological inves- 

 tigations, respecting the fundamental relations existing among animals, differed con- 

 siderably from the ideas then prevailing. In order, therefore, to be correctly 

 understood, he begins, with his accustomed accuracy and clearness, to present a 

 condensed account of those opinions with which he disagreed, in these words: — 



"Few views of the relations existing in the organic world have received so 

 much approbation as this : that the higher animal forms, in the several stages of 

 the development of the individual, from the beginning of its existence to its 

 complete formation, correspond to the permanent forms in the animal series, and 

 that the development of the several animals follows the same laws as those of 

 the entire animal series; that consequently^ the more highly organized animal, in 

 its individual development, passes in all that is essential through the stages that 

 are permanent below it, so that the periodical differences of the individual may 

 be reduced to the differences of the permanent animal forms." 



Next, in order to have some standard of comparison with his embrj'ological 

 results, he discusses the relative position of the different permanent types of ani- 

 mals, as follows : — 



"It is especially important that we should distinguish between the degree of 

 perfection in the animal structure and the type of organization. The degree 

 of perfection of the animal structure consists in the greater or less heteroge- 

 neousness of the elementary parts, and the separate divisions of a complicated 

 apparatus, — in one word, in the greater histological and morphological differen- 

 tiation. The more uniform the whole mass of the body is, the lower the 

 degree of perfection ; it is a stage higher when nerve and muscle, blood and 

 cellular tissue, are sharply distinguished. In proportion to the difference between 

 the.se parts, is the development of the animal life in its difleront tendencies; or, 

 to express it more accurately, the more the animal life is developed in its several 

 tendencies, the more heterogeneous arc the elementaiy parts which this life brings 

 into action. The same is true of the single parts of any apparatu.s. That organ- 



' I'cber Entwirkclungsgoscliiolitc lUr Tliit'i-o, 15;ier, KonigsbtTg, 1828, 4to. — See also Acta Nova 

 Bcobaciitung uml Uullexion von Dr. Karl Ernst von Acad. Leop. Ca;sar, vol. 13, and Meckel's Ai-eh., 1826. 



