15G FOURTH RE TOUT 1834. 



different branches of zoology, these attempts have on the whole 

 certainly advanced our knowledge of natural groups, and deve- 

 loped many affinities before unsuspected. At the same time it 

 is difficult to believe that there is not some truth at the bottom 

 of this theory, however erroneous it may be in its details ; and 

 that some of its details are erroneous, as w^ell as many of the 

 subordinate arrangements in the system which has been built 

 upon it, is almost certain, from many facts which have been 

 brought forwards of late years, as well as from that difference 

 of opinion* which exists with respect to these details amongst 

 those who admit the fundamental principles. Neither are these 

 fundamental principles entirely new. Mr. MacLeay has himself 

 shownf that his doctrines have all been in some measure ad- 

 vanced by authors prior to the publication of the Horce Ento- 

 mologicce ; which circumstance, while it tends to strengthen our 

 conviction that they have more or less of truth in them, does not 

 detract from Mr. MacLeay's mei'its in having developed them 

 far beyond what any of his predecessors had done. To him we 

 are certainly indebted for having pointed out the exact nature of 

 the difference between affinity and analogy in natural history, 

 however these two kinds of relation may have been observed by 

 former authors^. He was also the first to establish by proof 

 circular affinities. He has sufficiently demonstrated their exist- 

 ence in certain groups, to lead us to suspect that it is only our 

 as yet imperfect knowledge of forms, and the gaps necessarily 

 arising from the circumstance of many foriiis having become 

 extinct, which prevents us from tracing their existence gene- 

 rally. And these are by far the most important of Mr. MacLeay's 

 principles. Whatever of error there may be in the rest of his 

 views, whatever modifications already have been, or may yet 

 further be made in them, by the help of the above principles he 

 appears to have approached nearer than any before him to the 



• This difference of opinion more especially respects the determinate num- 

 ber. While Mr. MacLeay considers it as five, and Mr. Swainson as three, Mr. 

 Kirby is of opinion that it will turn out to be seven. {Introd. to Ent., vol. iii.p. 15.) 

 It must be stated that this gentleman has hitherto brought nothing forward in 

 support of this last number. It has, however, found an advocate in Mr. New- 

 man, who has also endeavoured to establish some other modifications of Mr. 

 MacLeay's theory. See a small tract, called Sphinx Vespiformis, published in 

 1832. 



f Linn. Trans., vol. xvi. p. 8. 



X I add this because, some time back, there was a controversy between M. 

 Virey and Mr. MacLeay on the question of priority with respect to the above 

 distinction. See a review, by the former, of some of Mr. MacLeay's opinions in 

 Btdl. des Sci. 1825. tom. iv. p. 275, in which M. Virey states having made this 

 distinction long before in the Notiv. Did. d'Hisl. Nat., Art. Animal. Mr. Mac- 

 Leay has replied to M. Virey in Zool. Jottrn., vol. iv. p. 47. 



