204 Mr. W. S. MacLeay's Examination of 



ated." Tliis, however, is clearly the essential characteristic 

 laid down in the law, ?inre a Negro " produces by certain 

 laws of generation others like himself," and yet is not very 

 generally accounted to be a distinct species. But I ought to 

 recollect, that in spite of Mr. Wilberforce, you have your 

 doubts on this particular point : that in fact it still remains 

 with you "the most difficult problem of all." 



You lay down as a " first principle of arrangement," that 

 " in Botany the characters of a Genus should be taken from the 

 parts of fructification, and in Zoology from such parts as are 

 indicative of structure and habits." Having myself, as you 

 know, dabbled a little in Zoology, and being pleased with the 

 sight of a really new definition, I am anxious to learn what 

 other zoological parts remain, in order that I may avoid them. 



To clear up the fog in which our poor brains are enveloped 

 when we attempt to distinguish a species from a genus, you 

 next inform us that " there is the same difference between a 

 genus and a species as instruments of reasoning, as between a 

 definition and a proposition in geometry." Now the differ- 

 ence between the latter is, that the proposition requires de- 

 monstration, and the definition not. I must therefore suppose 

 that this mode of illustration is " tit lucus a non lucendo," for 

 you have just before declared that species must " be brought 

 to the test of experiment," in other words, must be demon- 

 strated. 



It appears 3'ou do not regard genera as merely conven- 

 tional, but as actually founded in nature, as well as species. I 

 likewise consider genera *when iiro-perly defined^ to be founded 

 in nature, as I have elsewhere said ;* but I have not found even 

 these natural genera, upon the whole, to be so distinctly insu- 

 lated from each other as species. I will now, however, go 

 further than you, by stating that the groupes you object to, 

 such as Class, Order, Tribe, Cohort, and Family, are, when 

 properly defined, just as natural as Genera; and also that the 

 higher we ascend in the scale, and the more comprehensive 

 our groupes are, we may, in general, be assured, that in the 

 same proportion they are perhaps even more natural. Thus, 

 who will assert that Animals form a less natural groupe than 

 Vertebrata, Vertebrata than Mammalia, Mammalia than Ce- 

 tacea, or these last than the genus Balaena ? Even Linnaeus, 

 the infallible Linna3us, speaks of natural classes and natural 

 orders as distinct from artificial ones. No one, till now, has 

 ventured to call the classes of Mammalia, Birds and Fishes, 

 or the orders Lepidoptera, Coleoptcra and Diptera, ^'■gratui- 

 tous assumptions." Your doctrine, therefore, is really original ; 



* Sec Horac Enloniologica;, page 490. 



but 



