490 COLOUR OF SHELLS. 



with many vivid hues, those of the greater depth, though 

 their shells are almost as brightly coloured as the coverings 

 of their allies nearer the surface, have their animals for the 

 most part of an uniform yellow or reddish hue, or else en- 

 tirely white. 



" The chief cause of this increase of intensity of colour 

 as we ascend, is doubtless the increased amount of light 

 above a certain depth. But the feeding grounds of the 

 animals would appear to exert a modifying influence, and 

 the reds and greens may be in many cases attributed to the 

 abundance of nullipore, and of the Caulerpa prolifera, a 

 sea-weed of the most brilliant pea-green, the fronds of 

 which the Mollusca of that colour, such as Nerita viridis, 

 make their chosen residence."* 



And now I bid you a short farewell with the repetition of 

 my former advice, to learn the nomenclature of this little 

 corner of natural history, by an actual examination of ex- 

 amples in your own collection ; and you might conduct that 

 examination in such a sure way, that it will lead you to dis- 

 cover the position of the object in the system, and the name 

 it bears amongst those with whom you wish in future to 

 hold occasional converse. Listen to the words of one of the 

 greatest of men in modern times : 



" Natural history, in fact, is one of those sciences in which 

 genius is impotent, unless seconded by power; and the 

 efforts of power vain, unless its results are arranged by the 

 co-operation of genius. The names, which man is ordered 

 to impose, are not incoherent signs applied by chance to 

 some isolated objects. To render them appropriate and sig- 

 nificant, the objects, as it is said, must pass before the 

 namer ; in other words, he must compare these objects, 

 apprehend the relations of their similarity and difference, 

 and classify them ; which he cannot do unless he see them 

 together, and make himself intimately acquainted with them. 

 In short, to name well, taking the word in its fullest accep- 

 tation, it is necessary not only to know well, but, it may be 

 said, to know all. The superstition of the Cabalists be- 

 lieved in the magic power of names. This was a false con- 

 sequence of a principle, that names, were they perfect, 

 would represent the essence and aggregate of things. 



" Such is the object of this department of science, which 

 unreflecting minds would doom to contempt, under the name 

 of Nomenclature. To refute their assertions, it is only 

 necessary to repeat the fundamental condition which we 



* On Algean Invertebrata, in Reports Brit. Assoc. 1843, p. 172 3. 



