194 K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 



brain. The larva of the Frog has a true beak like Birds, and 

 before it loses its tail an intestine of a length such as is only 

 to be found permanently in a few forms of Mammals. The Frog 

 larva is at first tail-less, a condition that occurs only among the 

 highest Mammals ; even the adult Frog has an internal tail, for 

 we must so designate its long caudal vertebra. The Myriapods, 

 the Mites, and the Hydrachne have, when they creep out of the 

 egg, only three pair of feet, like the perfect condition of Insects 

 which undergo metamorphosis. Even if, contrary to my opinion, 

 it be maintained that the Arachnida are more highly developed 

 than the true Insects, yet every one will allow that Insects with 

 a metamorphosis are higher developments of the Myriapoda. 

 Such cases as these should by no means occur, if the develop- 

 ment of the higher animals consisted in passing through the 

 forms of the lower ones. 



5. We ought to see the organs or larger apparatuses make 

 their appearance in the different classes of animals in the same 

 manner as they are developed in the embryos of higher animals, 

 if we consider the former to be developed out of one another ; 

 this, however, is by no means the case ; the posterior extremity is 

 in most Fishes only perfect in its terminal member, while in the 

 embryo of the higher animals the proximal joint is first formed. 



6. Lastly, such parts as are found only in the higher animals 

 should arise very late in the course of development. But it is 

 not so. A few portions of the vertebral column, its centre and 

 arches, exist earlier in the Chick than every other part. How 

 then can the Chick ever have any similarity with an invertebrate 

 animal ? 



This remark, however, leads us nearer to our purpose, and 

 therefore at this point the attempt to discover the true relation 

 may be made. 



3. On the Mutual Relations of the different permanent Forms 



of Animals. 



In order to investigate the essential relations of the metamor- 

 phoses which occur in the development of the individual, I 

 must premise a sketch of the different forms of animals. I have 

 already in part treated of this subject in another place (Nova 

 Acta Acad. vol. xiii. part ii. pp. 739-762) ; but since the re- 



