ZOOLOGY xxvii 



true order ; and in so far as they do this, they are valid and 

 useful. But the hues of demarcation between these groups 

 are regarded by Lamarck as wholly arbitrary. You may, 

 for instance, take the first hundred species of the scale and 

 call it Class L : the second hundred species you may call 

 Class n. : but you would have been equally justified in 

 taking the first 120 species and calling them Class L, and 

 the second 120 Class IL In short, there is no real division 

 or break in the scale of animal nature. 



Hence, Lamarck refers to classes, orders, families, genera 

 as " parties de l'art," or devices introduced by art for human 

 convenience, and not corresponding to anything real in 

 nature. Yet he regarded these devices as absolutely essential 

 for introducing order into what would otherwise be a chaotic 

 jumble. We are thus forced to adopt either a schematic 

 classification or a " natural " classification : the former is 

 a mere grouping of animals by respect to certain characters 

 of no fundamental taxonomic importance ; the latter repre- 

 sents the series of species in their true order, and is only 

 artificial, says Lamarck, in so far as it breaks them into 

 groups. Since such subdivision of the series is a practical 

 necessity, he held that it is wise to apportion our classes, 

 orders, etc., in such a way that the gaps in our knowledge 

 fall between them, and do in fact create apparent groupings 

 in the animal world. 



Lamarck then proceeds to trace the essentials of a natural 

 classification, which shall be in correspondence with the 

 order of nature. The guiding principle must be the true 

 alB&nities (rapports) between animals. Their contiguity in 

 the series is to be determined, mainly by the resemblance 

 existing between their most " essential " organs, and to a 

 lesser degree by the resemblance between less " essential '* 

 systems of organs. By " essential " Lamarck means, in the 

 case of animals, essential to the maintenance of individual 

 life, and in the case of plants essential to reproduction. 

 He says that the most essential system, in the determination 

 of affinities, is the " organ of feeling," or nervous system ; 



