ON THE ART OF CLASSIFYING. 31 



Thus LlNN^EUS adopts six classes, of which the differences, 

 though founded on internal structure, have still reference to the 

 function of a part which is by no means common to all animals. 

 The number of LINNAEUS' Insects and Worms that have no heart 

 at all, is in fact at least as great as the number of those in which 

 it is present. The so-called Zoophytes, and the Intestinal Worms, 

 have no heart : in many animals vessels are already present before 

 a heart can be found : insects which undergo metamorphosis have 

 only a doubtful rudiment of a heart (the so-called dorsal vessel). 

 The physiological importance of the heart is consequently not of 

 that kind that it should be considered indispensable in the animal 

 economy, as appears to be tacitly assumed in this arrangement. 

 Moreover, in Amphibia the heart is provided not with one auricle 

 only, but with two, and many of the Worms have not merely a 

 ventricle, but also an auricle. Still the first four classes are so 

 truly characterised and so firmly founded in nature, that we may 

 well wonder that they were not in all times recognised, and not 

 earlier formed. That clear and accurate insight which charms 

 every one, and that simplicity to which all natter themselves they 

 can attain in their own province, are the true characteristics of 

 genius. LINNAEUS was less happy in his two last classes, as we 

 will shew more particularly. Moreover, it is not commendable 

 that the division is founded upon a single organ or system of 

 organs, as, for instance, those of circulation. In this way, indeed, 

 artificial divisions may be obtained, but not a natural method. 

 (See above, p. 29.) 



The arrangement of LINNAEUS, in these last times, has under- 

 gone various alterations, when men began, after the example of 

 CAMPEK, PALLAS, POLI, and others, to investigate the internal struc- 

 ture of animals: in which investigation CuviER 1 , the first anato- 

 mist of our age, by his incomparable achievements was especially 



at Leyden in large folio in 1735 : it consists of three tables, each containing one of the 

 three kingdoms of nature with some notices appended. He begins with the Mineral 

 Kingdom and ends with the Animal Kingdom. 



1 GEORGE LEOPOLD CHRETIEN FREDERIC DAGOBERT CUVIER, b. at Montb&iard 

 24 Aug. 1769, d. at Paris 13 May 1832. See my biography of this celebrated contem- 

 porary in the Bijdragen tot de Natuurkundicje Wetenschappen, ritgcgeven door H. C. 

 VAN HALL, W. YROLICK, en G. J. MULDER, vn. 1832. p. 298 333. Very important 

 for the history of CUVIER'S education are the letters addressed by him to C. H. PFAFF, 

 the friend of his youth, lately published at Kiel by Professor BEHN. 



