242 ESSAY ON CLASSIFICATION 



similar features in groups otherwise remote, as far as their anatomical 

 characters are concerned, whilst affinity is based upon similarity in 

 the structural relations. On account of the similarity of their locomo- 

 tion, Bats, for instance, may be considered as analogous to Birds; 

 Whales are analogous to Fishes on account of the similarity of their 

 form and their aquatic mode of life; whilst both Bats and Whales 

 are allied to one another and to other Mammalia on account of the 

 identity of the most characteristic features of their structure. This 

 important distinction cannot fail to lead to interesting results. Thus 

 far, however, it has only produced fanciful comparisons from those 

 who first traced it out. It is assumed, for instance, by MacLeay that 

 all animals of one group must be analogous to those of every other 

 group, besides forming a circle in themselves; and in order to carry 

 out this idea all animals are arranged in circular groups in such a 

 manner as to bring out these analogies, whilst the inost obvious affini- 

 ties are set aside to favor a preconceived view. But that I may not 

 appear to underrate the merits of this system, I will present it in the 

 very words of its most zealous admirer and self-complacent ex- 

 pounder, the learned William Swainson.*^ 



Tlie Horce Entomologies ,^^ unluckily for students, can only be thoroughly 

 understood by the adept, since the results and observations are explained in 

 different parts; the style is somewhat desultory, and the groups, for the most 

 part, are rather indicated than defined. The whole, in short, is what it professes 

 to be, more a rough sketch of the leading peculiarities of the great divisions of 

 animals, and the manner in which they are probably connected, than an accu- 

 rate determination of the groups themselves, or a demonstration of their real 

 affinities. More than this, perhaps, could not have been expected, considering 

 the then state of science, and the herculean difficulties which the author had to 

 surmount. The work in question has now become exceedingly scarce, and this 

 will be an additional reason with us for communicating occasional extracts from 

 it to the reader. Mr. MacLeay's theory will be best understood by consulting 

 his diagram; for he has not, as we have already remarked, defined any of the 

 vertebrated groups. Condensing, however, the result of his remarks, we shall 

 state them as resolvable into the following propositions: 1. That the natural 

 series of animals is continuous, forming, as it were, a circle, so that, upon com- 

 mencing at any one given point, and thence tracing all the modifications of 

 structure, we shall be imperceptibly led, after passing through numerous forms, 

 again to the point from which we started; 2. That no groups are natural which 

 do not exhibit such a circular series; 3. That the primary divisions of every large 

 group are ten, five of which are composed of comparatively large circles, and 



^Geography and Classification of Animals, pp. 201-205. 



"MacLeay, Horce Entomological, or Essays on the Anniilose Animals (2 vols., Lon- 

 don, 1819-1821). 



