INTRODUCTION. xxi 



entire group. Some are very close to the type, others differ from it 

 to such a degree that we might have failed to recognise the connec- 

 tion, were it not for the presence of intermediate links. These are 

 called aberrant forms. 



It may be asked, are the divisions, which are here indicated, 

 natural, i.e., marked out by nature, or, in other words, designed ? 

 That some of them are so, we may, I think, safely infer from the 

 example already quoted of the Vertebrata. Here we have at least 

 four, some say five, great divisions marked out by nature so broadly 

 that the distinctions are in most cases recognizable and patent to all 

 and, in each of these classes so clearly marked, that there are certain 

 divisions apparent even to the uninstructed ; such, for example, 

 among birds, are the Birds of Prey, Owls, Finches, Game birds. 

 Ducks, &c., &c. Many genera, too, are undoubtedly exceedingly 

 natural and clearly defined; and on the whole, I think, we may con- 

 clude that Nature herself (could we but correctly read her lessons) 

 has pointed out most of the divisions; or, in other words, has varied 

 each group, small as well as great, in a certain and definite method. 

 Many natural divisions however appear to grade into each other, and 

 have no definite limits ; yet, for purpose of study, we must assign 

 limits and characters; and the affinities, by which they are grouped, 

 must be judged of by as many and as constant characters as possible, 

 derived from all parts; but certain typical characters must be 

 assigned. 



There are at present above 8,000 species of birds known and 

 described, though much of the civilized world has yet to be explored. 

 XVhen this has been done, what the number may be it is difficult to 

 conjecture, but this large number has been arranged by Naturalists 

 into six large orders, founded entirely on the organs of manducation 

 and prehension. These are : 



I. Raptores, or birds of prey. 

 II. Insessores, or perching birds. 

 III. Gemitores, or pigeons. 

 IV. Rassores, or game birds. 

 V. Grallatores, or waders. 

 VI. Natatores, or swimming birds. 



