ilS HISTORY OF ZOOLOGY. 



It will appear, and indeed it hai'dly requires to be proved, that those 

 steps in systematic zoology which are due to the light thrown upon 

 the subject by physiology, are the result of a long series of labors by 

 various naturalists, and have been, like other advances in science, led 

 to and produced by the general progress of such knowledge. We can 

 hardly expect that the classificatory sciences can undergo any material 

 improvement which is not of this kind. Very recently, however, some 

 authors have attempted to introduce into these sciences certain princi- 

 ples which do not, at first sight, appear as a continuation and extension 

 of the previous researches of comparative anatomists. I speak, in par- 

 ticular, of the doctrines of a Circular Progression in the series of 

 affinity ; of a Quinary Division of such circular groups ; and of a relation 

 of Analogy between the members of such groups, entirely distinct from 

 the relation of Affinity. 



The doctrine of Circular Progression has been propounded princi- 

 pally by Mr. Macleay ; although, as he has shown, 13 there are sugges- 

 tions of the same kind to be found in other writers. So far as this 

 view negatives the doctrine of a mere linear progression in nature, 

 which would place each genus in contact only with the preceding and 

 succeeding ones, and so far as it requires us to attend to more varied 

 and ramified resemblances, there can be no doubt that it is supported 

 by the result of all the attempts to form natural systems. But whether 

 that assemblage of circles of arrangement which is now offered to 

 naturalists, be the true and only way of exhibiting the natural relations 

 of organized bodies, is a much more difficult question, and one which 

 T shall not here attempt to examine ; although it will be found, I think, 

 that those analogies of science which we have had to study, would not 

 tail to throw some light upon such an inquiry. The prevalence of an 

 invariable numerical law in the divisions of natural groups, (as the 

 number five is asserted to prevail by Mr. Macleay, the number ten by 

 Fries, and other numbers by other writers), would be a curious fact, if 

 established ; but it is easy to see that nothing short of the most con- 

 summate knowledge of natural history, joined with extreme clearness 

 oi view and calmness of judgment, could enable any one to pronounce 

 on the attempts which have been made to establish such a principle. 

 But the doctrine of a relation of Analogy distinct from Affinity, in the 

 manner which has recently been taught, seems to be obviously at vari- 

 ance with that gradual approximation of the classificatory to the phy- 



13 Linn. Trans, vol. xvi. p. 9. 



