ON THE ART OF CLASSIFYING. 35 



are not radiant, but are placed in this type on account of the 

 imperfection of their organisation alone. 



It is to YON BAER especially that we are indebted for a clear 

 insight into this distinction 1 . He considers the classes as sub- 

 divisions of the fundamental form or type, which differ in respect of 

 the higher or lower grade of organisation. We may conceive the 

 matter differently, thus : that every animal class is determined by 

 two factors, of which one is the type of organisation, the other the 

 perfectness of structure. The highest perfectness is in general 

 linked to the type of the vertebrates : yet how imperfect, how poor 

 (if I may use the term) the organisation may be, even in a verte- 

 brate animal, the anatomical investigation of ampliioxus lanceolatus 

 in recent times has taught us. That this little fish is in complexity 

 of organisation far surpassed by many insects and molluscs, cannot, 

 on unprejudiced examination, be denied. 



In the arrangement, therefore, of classes, we shall lay down as 

 our basis this idea of type of organisation, and shall thus avoid 

 separating that which is connected by natural transitions. We 

 begin with the Eadiata, because in this type organisation stands on 

 the lowest grade, and even the most perfectly organised radiates 

 are surpassed by a great, nay the greatest, number of Annulates 

 and Molluscs in complexity of organisation, variety of functions, 

 and multifarious enjoyment of life. Whether, after these, we pro- 

 ceed with the Annulata or the Mollusca, is in a certain sense indif- 

 ferent. Nature has not formed the creatures in a single ascending 

 rank. Were this the case, then would a single type necessarily 

 prevail in them all : yet even in the divisions (classes, orders and 

 families) belonging to a single type, we are not able to discover 

 such a simple ascent of organisation. The most perfect fish is not, 

 by proximate affinity, joined on to the least perfect of the reptiles : 

 nor the most composite bird to the most imperfect mammal. It 

 was a pleasing dream of the amiable BONNET 2 , that all creatures 



1 Beitrdge zur Kentniss der niedern Thiere, von Dr. K. A. v. BAER, Nov. Act. Cces. 

 L. C. Nat. Curios. Vol. xm. P. II. 1827. s. 523 762, especially s. 739 759; Ueber 

 Enlwickdungsgeschichte der Thiere. Beobachtung und Reflexion. 4. I. Konigsberg, 1828. 

 s. 207 219. In France also similar ideas were afterwards advanced by MILNE 

 EDWARDS. See ex. gr. his remarks in the new edition of LAMARCK : Histoire Nat. des 

 Ani. s. vert. I. Paris, 1835, pp. 335337, revised by him and DESHAYES. 



2 Contemplation de la Nature. (Euvres d'Hist. NatureUe et de Philosophic de CH. 

 BONNET. Tome vn. Neufchatel, 1781, 8vo. pp. 51 55, and other places. 



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