TESTACEOUS FISH. 



849 



The usual way of accounting for the dif- 

 ferent colouring of shells, which seems to me 

 erroneous, is this ; in the body of every one 

 of these animals, several streaks are discerned 

 of a different colour from the rest. " This 

 variety," say they, " is an incontestable proof 

 that the juices flowing from these parts will 

 be also of a different hue ; and will con- 

 sequently tinge that part of the shell which 

 their slime composes of a different colour." 

 But this system, as was observed before, is 

 overthrown by the fact, which discovers that 

 only the outer surface of the shell is tinged ; 

 whereas by this it would have been coloured 

 throughout ; nay, by this system, the internal 

 parts of the shell would be stained with the 

 most vivid colouring, as being least exposed 

 to the external injuries of the element where 

 it is placed. But the truth is, the animal 

 residing in the shell has none of these various 

 colours thus talked of: its slime is a simple 

 pellucid substance; and the only marblings 

 which appear in its body, are the colour of the 

 food, which is seen through its transparent in- 

 testines. We must, therefore, account for the 

 various colouring of its shell upon a different 

 principle. 



If, as I said, we examine the cabinets of the 

 curious, we shall find shells with various 

 and beautiful colouring ; we shall find them 

 generally furnished with a white ground, 

 tinctured with red, yellow, brown, green, and 

 several other shades and lovely mixtures, but 

 never blue. Shells are of almost all colours 

 but blue. The reason seems to be obvious ; 

 for blue is the colour which sea-water changes. 

 A piece of silk, or a feather, of this colour, 

 put into an infusion of salt, urine, or nitre, lose 

 their tint entirely. Now may not this give 

 us a hint with respect to the operation of 

 nature in colouring her shells ? May we not 

 from hence conclude, that sea- water is effica- 

 cious in giving colour, or taking it away ? 

 That, to produce colour, the animal not only 

 furnishes its juices, but the sea or the earth 

 that mixture of substance which is to unite 

 with them? Neither the animal slime alone, 

 nor the external earthy or saline substances 

 alone, could produce colours; but both united, 

 produce an effect which neither, separately, was 

 possessed of. Thus shells assume every colour 

 but blue ; and that sea-water, instead of pro- 

 ducing, would be apt to destroy. 



From hence, therefore, it appears, that the 

 animal does not alone tincture its own shell ; 

 but that external causes co-operate in contri- 

 buting to its beauty. It is probable that, 

 from the nature of its food, or from other cir- 

 cumstances unknown to us, the external 

 layers of its slime may be of different consis- 

 tences ; so, as when joined with the particles 

 of earth or salt that are accidentally united 



with them from without, they assume various 

 and beautiful hues. But the internal layers, 

 which receive no foreign admixture, still pre- 

 serve the natural colour of the animal, and 

 continue white without any variation. 



Thus far we see that the animal is not 

 wholly the agent in giving beauty and colour- 

 ing to its shell : but it seems otherwise with 

 respect to its convolutions, its prominences, and 

 general form. These entirely depend upon 

 the art of the animal ; or rather upon its in- 

 stincts; which, in the same kinds, are ever 

 invariable. The shell generally bears some 

 rude resemblance to the body upon which it 

 has been moulded. Thus, it is observable in 

 all sea-shells, that if the animal has any 

 tumour, or excrescence on its body, it creates 

 likewise a swelling in that part of the incrus- 

 tation to which it corresponds. When the 

 animal begins to alter its position, and to 

 make new additions to its apartments, the same 

 protuberance which had raised the shell before 

 in one part, swells it again at some little dis- 

 tance; by which means we see the same in- 

 equality, in a spiral line, all round the shell. 

 Sometimes these tumours of the animal are so 

 large, or so pointed, that those which rise 

 over them, in the incrustation appear like 

 horns : after this the animal disengages itself 

 from its first . cavities ; and then, by fresh 

 evacuations, assumes a new set of horns; and 

 so increases the number in proportion to its 

 growth. If, on the other hand, the body hap- 

 pens to be channelled, the shell that covers it 

 will be channelled likewise ; if there be any 

 protuberances in the body, which wind in a 

 spiral line about it, the shell will likewise have 

 its tumours and cavities winding round to 

 the end. 



In this manner, as the animals are of vari- 

 ous forms, the shells exhibit an equal variety. 

 Indeed, the diversity is so great, and the 

 figures and colours so very striking, that 

 several persons, with a kind of harmless indo- 

 lence, have made the arrangement of them the 

 study and the business of their lives. Those 

 who consult their beauty alone, take care to 

 have them polished, and to have an external 

 crust, or periosteum, as Swammerdam calls 

 it, scoured off from their surfa'ces by spirit of 

 salt. But there are others that, with more 

 learned affectation, kept them exactly in the 

 state in which they have been found, with 

 their precious crust still round them. The 

 expense men have sometimes been at, in mak- 

 ing such collections, is amazing ; and some 

 shells, such as the Stairs-shell, or the Admiral- 

 shell, are not more precious for their scarce- 

 ness, than pearls are for their beauty. Indeed, 

 it is the scarcity, and not the beauty of the 

 object, that determines the value of all na- 

 tural curiosities. Those shells that offer but 



