K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 221 



phological differentiation ; 2ndly, by the metamorphosis of a 

 more general form into a more special one. 



Corollaries to the Fifth Scholium. 



The history of development is the true source of light for the 

 investigation of organized bodies. At every step it finds its ap- 

 plication, and all the conceptions which we have of the mutual 

 relations of organized bodies must experience the influence of 

 our knowledge of development. It would be an almost endless 

 task to demonstrate this for all branches of investigation. Since, 

 however, those conceptions must spontaneously modify them- 

 selves so soon as the course of development is otherwise under- 

 stood, we may be permitted to bring forward a few points in 

 order to exhibit the influence of the view here set forth, and 

 thereby to justify the length at which it has been given. I have 

 endeavoured also to arrange these additions or appendices, so 

 that those which come first may contribute to the understanding 

 of the subsequent ones ; yet I have not been able always to suc- 

 ceed in doing this without intercalating many explanatory epi- 

 sodes. The reader will have also to complain of repetitions. 

 The greatest repetition of all however is, that all these considera- 

 tions are nothing more than reflexions of the contents of this 

 Scholium. 



FIRST COROLLARY. Application of this Scholium to the 

 Doctrine of Arrests of Development. 



It is no longer necessary to demonstrate that monstrous 

 growths can only be understood by knowing the normal course 

 of development. But I may be permitted to say a word con- 

 cerning arrests of development, since sometimes the understand- 

 ing of these malformations has been considered to be insepa- 

 rable from the view of the progression of the higher through 

 the lower forms of animals ; and it might thence be believed that 

 a contradiction of the latter view contradicted the doctrine of 

 arrests of development. This doctrine, however, is too well 

 based to be shaken by any alteration in the views which are en- 

 tertained with regard to the differences of form in the course of 

 the development of the higher organisms. Yet these malforma- 

 tions must not be regarded as the permanent forms of some other 



