RKl'ORT ON ZOOLOGY. 155 



papers) he has conceived to make a nearer approach to the true 

 natural system, endeavoured to work out an amended arrange- 

 ment of some of the principal groups of birds. The modifica- 

 tions which Mr. Swainson has been led to make in this work of 

 Mr. MacLeay's principles are these. He conceives, that although 

 every natural group is resolvable into five others, the primary 

 division is into three, each of M'hich forms its own circle : he 

 thus rejects Mr. MacLeay's binary distribution of his five groups 

 into typical and aberrant, which last not forming circles, would 

 seem to be rather at variance with his own principles. He has 

 also stated more precisely the law by which it appears to him 

 the relations of analogy are governed. It is thus given : The 

 contents of every circle or group are symholically represented, 

 by the contents o/all other circles in the same class of animals ; 

 this resemblance being strong or remote, in proportion to the 

 proximity or the distance of the groups compared* . This prin- 

 ciple, which Mr. Swainson terms the theory of representation, 

 he considers as affording the only certain test of a natural group. 

 Mr. MacLeay had considered such a test to be afforded by a 

 group returning into itself, which Mr. Swainson thinks not 

 suflBcient, on the ground that there is not one group in three 

 which c«n be so tested ; this arising partly from our superficial 

 acquaintance with forms, and partly, as he believes, from there 

 being many real gaps in the chain of continuity. It will be 

 observed that Mr. Swainson has been the first to bring forward 

 any nevt^ laws of arrangement at all analogous to those originally 

 developed in the Horce Entomologies ; and it is right to state, 

 that the above are not mere hypothetical deductions, but have 

 resulted from eight years' close analysis of the order Insessores 

 in the class of birds, with reference to which order principally 

 it is that he has illustrated them in the Fauna Boreali-Ame- 

 ricana. 



It is evident that the necessary limits of this Report foi'bid any 

 further analysis of Mr. MacLeay's theory, or of the several works 

 and memoirs above referred to. To some of these last I shall 

 have further occasion to allude afterwards. What has been ad- 

 vanced may tend, however, to point out the influence which this 

 theory has had over our own naturalists ; and if they have not 

 been all equally successful in their endeavours to apply it to 



• M. Isidore Geoffroy St. Hilaire, in France, has also attended to the subject 

 of analogies in zoology, and endeavoured to refer them to some general law. The 

 reader is referred to a note attached to a memoir published by him in the Nouv. 

 Ann. (hi Miis., torn. i. p. 380, in which he has given a slight sketch of his views 

 on this point. He proposes to make it the subject of a distinct paper at some 

 future opportunity. 



