246 ESSAY ON CLASSIFICATION 



whom the civilized world acknowledges as the founders of modern 

 Embryology. 



The principles of classification propounded by K. E. von Baer 

 seem never to have been noticed by systematic writers, and yet they 

 not only deserve the most careful consideration, but it may fairly be 

 said that no naturalist besides Cuvier has exhibited so deep an in- 

 sight into the true character of a natural system, supported by such 

 an extensive acquaintance with the subject, as this great embryolo- 

 gist has in his "Scholien und Corallarien zu der Entwickelungsge- 

 schichte des Hiihnchens im Eie."^^ These principles are presented in 

 the form of general proportions, 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 Baer had arrived by his embryolog- 

 ical investigations respecting the fundamental relations existing 

 among animals differed considerably 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 com- 

 plete 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 em- 

 bryological results, he discusses the relative position of the different 

 permanent types of animals, as follows: — 



It is specially 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 heterogeneous- 



^See von Baer, Ueber Entwickelungsgeschichte der Thiere (1828). See also his 

 "Beitrage zur Kenntniss der niedern Thiere," Nova Acta Academia Caesarea Leopol- 

 dino-CarolincE, XIII (1827), 525-762, and "Ueber das aiissere und innere Skeleton," 

 Archiv fiir Anatomie und Physiologic v. J. F. Meckel, I (1826), 327-376. 



