xviii PREFACE. 



of the organ which observation had shown to define the groups. 

 The naturalist, thus enabled to place his subject in its pi'oper 

 class or order, is not concerned, as such, in knowing the homo- 

 logical or transcendental relations of the part or character which 

 has afford ed him the means of effecting what he wished to do. 



Lixx.kus, to whom mainly is due the discernment of the power- 

 ful instrument of well-defined terms in acquiring a systematic, 

 Science of Nature, and to whom we owe our best knowledge of 

 its use, so named the guiding parts of plants and animals, for such 

 arbitrary or special application, in botany and zoology : to this 

 end he differentiates the ' bract,' the ' spath,' the ' sepal,' the 

 ' petal,' from the ' leaf,' as things distinct. 



What would be thought of the botanical critic who, quoting the 

 definition of the flowers of Cyperaceous plants, as consisting, for 

 example, of ' glumes,' should meet the statement by affirming that 

 they were ' nothing but little bracts,' and who, then, with a show 

 of profoimder research, should proceed to expound the 'bract' as 

 being the first step by which the common leaf is changed into a 

 floral organ ? The answer is obvious. But what next might be 

 said, if it were pointed out that the objector had obtained this 

 very notion from the ' Prolepsis Plantarum,' or other homological 

 writings of the author criticised, where such philosophical con- 

 siderations, foreign to the classificatory work, were the proper aim 

 and object ? So, with regard to the zoological definitions and 

 characters of Cuvier. Those which I have cited are open to the 

 opposite averment that, ' The " hind hands " of the Quadrumana 

 are nothing but " feet ; " ' and the contradictor might then proceed 

 to demonstrate, with much show of original research, the homology 

 of the ' astragalus,' ' calcaneum,' ' cuboides,' ' cuneiform bones,' 

 &c, in order to establish his discovery that a hand and foot are 

 all one. 



It is true that if the homological descriptions in the ' Lecons 

 d'Anatomie Comparee ' had been quoted, as well as the zoological 

 definitions in the ' Regne Animal,' the immortal author of the 

 latter work would be shown to have had previous possession of 

 the pretended discovery. Moreover, in the ' Cinquicme Lecon, 



