256 History of Conchology. 



though he sometimes drops a hint on the subject, which makes us 

 almost helieve that he was capable of better things, had he had courage 

 to have made the attempt. * In relation to the mollusca he clearly 

 saw the impropriety of making the presence or absence of the shell 

 an ordinal character ; and he knew, vaguely it may be, the affinity 

 between the bivalvular mollusca and the Tunicata. " For what" — 

 we translate his words — " are the Testacea but mollusca furnished 

 with a shell, and what are mollusca but Testacea destitute of it ? 

 There is the most exact agreement of the tenants of the univalve 

 shells which are called Helices with the naked slugs ; and an agree- 

 ment not to be overlooked of bivalves with the Ascidia ; and the very 

 error of our predecessors, who said that slugs were merely snails which 

 had crept out of their shells, proves their near affinity. Besides the 

 insensible but evident transition of nature from the naked Limax to 

 the testaceous — passing from the former, which at most has the mere 

 rudiment of an internal shell to the latter by means of the Buccinum 

 (Lymnsea) glutinosum, which conceals its membranous shell under 

 a fleshy mantle, supports plainly our opinion. Therefore I do not 

 doubt that a future age will join together the naked slugs and the 

 shelled snails, which authors have separated into different orders." 

 " If we wish," he writes in another place, " properly to know and 

 discriminate natural objects, they must be considered in every point 

 of view and in all states, so far as human imbecility will permit. The 

 attainment of knowledge is thus indeed rendered more difficult, but 

 at the same time more pleasant and accurate ; genera indeed are mul- 

 tiplied, but by this way only, if by any, can species ever be determin- 

 ed. This is the alpha and omega of our labours, since systems and 

 methods and genera are arbitrary and framed by the narrow limits of 

 our knowledge. Nature acknowledges one division of created bodies 

 only — the living and brute matter — spurning for the most part the 

 arrangements of systematists into classes and orders, families and 

 genera, and her productions are often so affined that their limits can 

 never be strictly fixed. Characters derived from the interior and ex- 

 terior structure of bodies deceive us not solely in the higher divisions ; 

 and even the manner of life and the mode of propagation do not af- 

 ford any certain distinctions either in those races which are visible 

 or in those which are invisible to the naked eye. There is therefore 

 only one family, and one Father of all, who has marked with a con- 

 stant character all species whatever from the Monad to the turret- 



* His ' Method,' as detailed by himself, is as artificial as the Linnaean, and ac- 

 tually less in harmony with the animal organization. 



4 



