INTRODUCTION. xxxi 



understood and appreciable. Not so, however, the 

 analogies exhibited by many species and groups to others, 

 perhaps very distantly related. These may be resem- 

 blances of structure, or of colour, or of habits. Some 

 naturalists explain them by expressing their belief that in 

 every group, great or small, there are certain types of 

 structure, offering fixed characteristic marks, and that 

 analogies are, simply, the representation in one group of a 

 certain type in another ; or, to put it in other words, that 

 analogous groups or species simply occupy a corresponding- 

 place in their respective classes, orders, or families. This 

 theory of representation has, perhaps, been carried out, to 

 too great an extent, by certain writers, but, nevertheless, it 

 appears to be founded on nature ; and the existence of 

 these, often unexpected, analogies between distant groups 

 and species, clearly manifests the unity of the plan of the 

 animal creation. According to Mr. Darwin's views, such 

 analogies might be explained on the supposition that the 

 resemblances were due to some remote ancestral orio^in.* 



The colours and markings of some birds appear 

 to be repeated in other groups ; and, in most natural 

 divisions, great variety of form of bill, and also of other 

 parts is exhibited, representing several distinct types; and, 

 in some, more distantly related, groups, analogy is sho^vn 

 by habits, by the color of the eggs, by seasonal change of 

 plumage, &c., &c. Many examples of analogy will be 

 pointed out in the present work. 



On beginning at any point in any series of beings, and 

 tracing, step by step, the scale of affinities, we soon find that 

 the supposed chain is interrupted, and that branches strike 



* If his theory be ever traced out in detail, this subject may be the mean- of testing 

 it thoroughly. 



