THE ARCHIPELAGO OF BREHAT. 97 



seems to have become indistinct. Now, these modi- 

 fications of type may be the result of three different 

 causes, acting either conjointly or separately. The 

 distinctive characters may have been partly or 

 wholly obliterated ; they may be intensified, or lastly 

 they may be complicated with extraneous charac- 

 teristics, whose tendency is either to destroy existing 

 relations or to establish new affinities. As Ions* as 

 these alterations do not pass beyond certain limits, 

 the animal, although he has to some extent departed 

 from his ideal type, still bears some affinity to it ; 

 but once pass these limits, and we have a new type. 

 When the changes to which we refer result from 

 the suppression of characters which are essential to 

 the first group, or when different or even opposite 

 characters are manifested, the types can obviously 

 exhibit only very slight affinity with one another. 

 Such is not the case, however, when the modifications 

 arise solely from the exaggeration or diminution 

 of an existing character. Then the new type will 

 be merely a derivative of the former: and however 

 great the apparent diversities by which it is dis- 

 tinguished may be, the source from which it has 

 emanated will always admit of being traced. Thus, 

 by way of illustration, we may instance Mammals, 

 Birds and Fishes, which all belong to one primitive 

 type, that of the Vertebrata, although they form three 

 well marked and distinct types. On the other hand, 

 we may cite the bat, which moves through the air, 

 and the whale, which pursues its course through the 

 waves of the sea : yet the first is not on this account 

 a bird, nor is the second a fish, but both are mammalcJ 



VOL. I. H 



