PEDIGREES AND FAMILY TIES. 205 



we should have a difficulty in distinguishing 

 between the reptile and the bird. 



Furthermore, we shall see that evolution is 

 not always progressive, on the contrary it is 

 sometimes retrogressive. We shall also learn 

 something of what we may call the law of 

 correlated variation. 



Concerning this Mr Darwin writes, " In man, 

 as in the lower animals, many structures are so 

 intimately related, that when one part varies, so 

 does another, without our being able, in most 

 cases, to assign any reason. We cannot say 

 whether the one part governs the other, or 

 whether both are governed by some earlier 

 developed part." Thus, pigeons with feathered 

 legs have the outer toes webbed. 



Let us turn now to the question of the birds' 

 pedigree, and, so far as is possible, trace out their 

 relationships one to another. 



The oldest bird of which we have any record 

 is that known as the Archceopteryx, meaning the 

 ancient-winged one. It is sometimes called the 

 lizard-tailed bird. The figure (p. 207) is a restora- 

 tion made by the writer, and is based on a study 

 of the fossil in the Berlin and London Museums. 



All that we know of this bird is gathered from 

 the remains of two fossils found in the Solenhofen 

 Lithographic Stone of Eichstadt in Bavaria. The 

 first of these was discovered in 1861, and is now 

 in the British Museum. The other was found in 

 1877, and it rests in the Berlin Natural History 

 Museum. 



. In the London specimen the hind-limb and 

 tail only are really well preserved ; whilst, in the 



