230 K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 



is spoken of, under the supposition that there is a progressive 

 development for every organ, from the Monad to Man, and that 

 this development is realized in accordance with the order of 

 progression of the animals, the particular exceptions from which 

 are now given. If, however, the organs are modifications of 

 fundamental organs, and these differ according to the scheme 

 of development (compare the following Corollary), there would 

 appear to be an erroneous assumption in this very supposition. 

 I believe, therefore, that if comparative anatomy is to be directed 

 to the ascertainment of the laws of formation, the only proper 

 way is, besides the constant reference to a fundamental type to 

 which the whole animal belongs, to compare the organs by 

 themselves in their different forms, as Burdach has attempted to 

 do in his g Physiology/ without arranging the forms in the same 

 order as the animals to which they belong would take in accord- 

 ance with their perfection in other respects. We shall thus 

 perceive how the general structure of the whole body of an ani- 

 mal, or its relation to the external world, operates in modifying 

 the form of particular organs, and so prevent ourselves from 

 being misled by prejudices. 



That, however, these retrogressions in the development of 

 organs are only an appearance which depends upon a pre- 

 supposed uniserial development, is rendered most obvious by 

 their disappearance, if we arrange the animals according to 

 another organic system than that which was previously used as 

 a base. I bring forward one example out of many. If I am 

 persuaded that the Articulata are to be arranged in a progress- 

 ively developed series, and dispose them according to the de- 

 velopment of the vascular system, I may order them thus : 

 True Insects, Myriapoda, Arachnida, Annelida. In this case 

 the eyes are retrogressive through the series. Of the respiratory 

 organs, and the vascular system besides, it is at once intelligible 

 that the one appears retrogressive with respect to the other, since 

 these systems are antagonistically related. If I consider them 

 as modifications of a fundamental type, in which sometimes 

 one and sometimes the other system is more changed from the 

 simple fundamental form, then all retrogressions disappear. 



What I have here said of the Articulata, in order to select an 

 obvious example, holds good not of them alone, n.or merely of 



