K. E. VON BAER.— PHILOSOPHICAL FRAGMENTS. 219 



I have been able to discover against the view in question, can. 

 have little weight so long as no internal differences in the larvae 

 have been demonstrated. 



For the simple reason, that the embryo never passes from one 

 principal type to another, it is impossible that it can pass suc- 

 cessively through the whole animal kingdom. Our Scheme, 

 however, shows at once that the embryo never passes through 

 the form of any other animal, but only through the condition of 

 indifference between its own form and others ; and the further 

 it proceeds, the smaller are the distinctions of the forms between 

 which the indifference lies. In fact, the Scheme shows that the 

 embryo of a given animal is at first only an indeterminate Ver- 

 tebrate, then an indeterminate Bird, and so forth. Since at the 

 same time it undergoes internal modification, it becomes in the 

 whole course of its development a more and more perfect 

 animal. 



However, it may be objected here, if this be the true law of 

 development, how comes it that so many good reasons could be 

 adduced for that which has been previously in vogue ? This may 

 be explained readily enough. In the first place, the difference 

 is not so great as it looks at first sight; and in the second, I 

 believe that an assumption was made in the latter view, and it 

 was afterwards forgotten that it had not been demonstrated ; 

 but especially, sufficient stress was not laid upon the distinction 

 between type of organization and grade of development. 



Since, in fact, the embryo becomes gradually perfected by 

 progressive histological and morphological differentiation, it 

 must in this respect have the more resemblance to less perfect 

 animals the younger it is. Furthermore, the different forms of 

 animals are sometimes more, sometimes less remote from the 

 principal type. The type itself never exists pure, but only 

 under certain modifications. But it seems absolutely necessary 

 that those forms in which animality is most highly developed 

 should be furthest removed from the fundamental type. In all 

 the fundamental types, in fact, if I have discovered the true ones, 

 there exists a symmetrical {gleichmdssige) distribution of the 

 organic elements. If now predominant central organs arise, 

 especially a central part of the nervous system, according to 

 which we must principally measure the extent of perfection, the 



