K. E. VON' BAER. PHILOSOPHICAL FRAGMENTS. 191 



circumstance their embryonic condition, therefore, differs from 

 their permanent state, if it had an analogue anywhere in the 

 animal series, it must be found almost always among the lower 

 animals. 



That, however, a few correspondences should be found be- 

 tween the embryonic condition of certain animals and the perfect 

 condition of others appears to be necessary, and of no particular 

 importance. They could not be wanting, since the embryos do 

 not lie without the sphere of the animal world, and since the 

 variations of which the animal body is capable are determined 

 for each form by an internal connexion and mutual reaction of 

 its separate organs, whence certain repetitions become necessary. 



To convince oneself that such a doubt is not wholly without 

 its weight, let it be imagined that Birds had studied develop- 

 ment, and that it was they who in turn investigated the structure 

 of the adult Mammal and of Man. Should we not find some- 

 thing of this sort in their physiological handbooks ? ^^ Those 

 four-legged and two-legged animals have much resemblance to 

 embryonic forms, for their cranial bones are separated, and they 

 have no beak, just like us during the first five or six days of in- 

 cubation : their extremities are a good deal alike, as ours are for 

 about the same period ; there is not a single true feather over 

 their whole body, but only delicate feather- shafts, so that we, as 

 fledgelings, are more advanced than ever they are ; their bones 

 are hardly at all brittle, and like ours during youth contain no 

 air at all; they have no trace of air-sacs, and their lungs are not ad- 

 herent, like ours at the earliest period ; they have no crop ; their 

 proventiculus and gizzard are more or less compounded into a 

 single sac ; evidently arrangements which in us are only trans- 

 itory, and the nails are in most of them as clumsily broad as in 

 us before we break the shell ; the Bats alone — seemingly the 

 most perfect among them — have any power of flight, which is 

 quite absent in the rest. And these Mammals, which for so 

 long a period after birth cannot find their own food, and which 

 are unable to raise themselves from the earth, must pretend for- 

 sooth that they are more highly organized than we !" 



If it be a law of nature that the development of the individual 

 essentially consists in passing through the permanent forms of 

 lower animals, it must follow — 



