222 K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 



animal which the embryo had to pass through, but simply as a 

 partial stoppage at an earlier stage of their own development. 

 At times unquestionably there exists an obvious similarity with 

 some permanent form in particular parts ; but it is as readily 

 demonstrable that this similarity is not the condition of the mal- 

 formation, but the result of other relations, either, 1st, because 

 that form is nearer the fundamental type, in which case any 

 stoppage at an earlier period of development must necessarily 

 approximate the higher form to it ; or, 2ndly, because the altered 

 formative conditions may approximate the formative conditions 

 of the same part in another animal. Thus, for example, the nose 

 in Man is sometimes elongated into a proboscis, which reminds 

 one of the snout of a Pig. But the human nose never passes 

 through any stage of development in which it resembles the 

 snout of a Pig ; on the other hand, the Pig's snout, at the fourth 

 week of embryonic life, is not only similar to that of a human 

 embryo at an early period, but is in fact much more like the 

 nose of the adult Man than at a later period. 



This relation agrees perfectly with the general law. The nose 

 of air-breathing Mammals in general does not project beyond 

 the jaw. Both the peculiarity of the Pig's snout, therefore, and 

 that of the human nose, arise subsequently without any transi- 

 tion of the one form through the other. If then a Man has the 

 snout of a Pig, it is no arrest of development, but the conse- 

 quence of an abnormal development, which has a result like that 

 in the Pig, where it is normal. While we are speaking of the 

 abnormal forms of the nose, I will call to mind the "Wolfs 

 jaws/' an indubitable arrest of development, but which is cer- 

 tainly no stoppage at any earlier form of animal. 



SECOND COROLLARY. Application of the present View to the 

 Determination of the separate Organs in the different Forms 

 of Animals. 



A closer acquaintance with the history of development will 

 sooner or later furnish us with the sole safe grounds in the de- 

 termination of the fitting denominations for, and in forming a 

 just judgment of, the organic parts of the different forms of 

 animals. At present a little may be done in this direction. 



Since, in fact, every organ becomes what it is only by the 



