12 INTRODUCTION TO 



have been distinguished by the terms Class, Genus, Species, and varieties 

 of the Species. The first and third are easily distinguished from each 

 other, as they are at the greatest actual distance ; but it is often 

 difficult to distinguish between the second and third; as also of the 

 third itself, whether it be a variety of the Species or only belonging to 

 the Genus. 



This is like the gradations of shade, the two extremes having the 

 least affinity : but it may not in all cases be so clear how far the two 

 last in affinity are in all their parts really distinct ; that is, it may not 

 be clear what is a distinct Species of any Genus, they being so nearly 

 allied in their affinities both in appearance and number. 



By Species I believe we now mean, things that have the same rela- 

 tionship in their most essential properties, however they may differ in 

 others. Animals breeding in the full extent of that process constitute 

 the species, although they may differ in some of their parts or other 

 circumstances ; but which [differences] are less essential, only consti- 

 tuting a variety. These varieties in the same species are much greater 

 in the domesticated animals than in those that are wild ; and this ap- 

 pears to arise from the unnatural life the domestic animals lead, 

 giving changes to the constitution so as to affect propagation. Another 

 cause for it will also be, the preservation of, and the endeavour to pro- 

 pagate, any accidental variety that may take place [in the domestic 

 animal] which might be lost in the wild, or at least not cultivated by 

 human industry, this seldom being in man's power. 



Of Animal Matter. 



Every thing in Nature is directly classible, and as most things bear 

 a relation to some other, such relationships are also classible, and that 

 according to their nearness. 



' Species ' is the immediate or direct and ultimate class, and is the 

 common term for anything that appears to be indivisible or immutable 

 (it is here to be observed that I do not mean simply species of matter); 

 but which may vary in a number of other properties, such as being 

 either simple or compound. If it be simply matter, then it is strictly 

 a species of matter, and cannot in itself vary but when making one part 

 of a compound : and, if it be a compound, then it is a property of that 

 compound arising out of the combination that forms the species ; and, if 

 decomposed, it is no longer that species of compound, but may form 

 many. A simple species of matter we are probably not acquainted 

 with ; but many species arising from combination we are well ac- 

 quainted with, as water, acids, alkali, &c. ; and we know the species 



