186 INTRODUCTION. 



groups form the passage of orders to orders, of families to families, do the 

 typical groups themselves pass into these aberrant groups, and so in- 

 sensibly, that, at certain stages, the dividing line between them is rather 

 conventional than distinctly indicated by Nature. This, however, is not 

 all ; each natural group is not only thus circular, returning into itself, and 

 linked by points of inosculation to other groups, but each group has its 

 analogues in the groups of other orders, and of other classes. Mr. Vigors, 

 alluding to his researches in ornithology, observes : "I discovered, as I 

 advanced, that the larger, or primary groups, into which it (the system of 

 ornithology) arranged itself, were connected together by an uninterrupted 

 chain of affinities ; that this series, or chain, returned into itself, and that 

 the groups of which it was composed, preserved, in their regular succes- 

 sion, an analogy to the corresponding groups, or orders, of the contiguous 

 classes of zoology. I equally detected the existence of the same principle 

 in most of the subordinate sub-divisions, even down to the minutest, to a 

 degree, at least, sufficiently extensive to afford grounds for asserting its 

 general prevalence." In these views, as well as in those which regard a 

 quinary arrangement of the greater and the subordinate circles, Mr. Vigors 

 strictly coincides with Mr. Mac Leay ; and he elsewhere observes, com- 

 menting on a passage in the writings of that eminent naturalist, " If the 

 natural groups, into which the animal kingdom is divided, bear a uniform 

 analogy to each other, a principle which is among the most important of 

 those in the system which I wish to illustrate, it is a necessary consequence 

 that their number should be definite. The primary groups of those de- 

 partments of the animal kingdom which have hitherto been investigated, 

 have been ascertained to be limited to five ; and the first great divisions of 

 birds will be found to branch out in a similar number." 



The following is a series of the orders of the Mammalia, according to 

 the views of Mr. Mac Leay ; adapted analogically to that of Birds, as given 

 by Mr. Vigors. (Part i. vol. xvi. p. 32, of Linn. Trans.) 



MAMMALIA. AVES. 



1. FER^E, carnivorous . . corresponding to 1. RAPTORES. 



2. PRIMATES, omnivorous 2. INSESSORES. 



3. GLIRES, frugivorous 3. RASORES. 



4. UNGULATA, frequenting the vicinity of water . 4. GRALLATORES. 



5. CETACEA, aquatic 5. NATATORES. 



The reasoning, upon which these orders are paralleled as analogues, 

 or representatives of each other, is, in many instances, we think, totally in- 

 admissible. The Ungulata (or hoofed mammals), and the Grallatores (or 

 wading birds), are regarded, for instance, as the analogues of each other, 

 because we find both to " contain examples of the longest legs, in propor- 

 tion to the body, witness Cameleopardalis and Himantopus (Stilt-plover). 

 Both orders present us, in groups, not exactly aquatic, with instances of the 



