Chap. V. 
C O N C H O L 6 G Y. 
Parts of 
Shells, &■ c. 
v"*~ 
91 
Seeming 
exception, 
Of the Con- the animal’s body, is itfelf blade or brown, that form- 
ftituent ec j between the ftripes is white or citron, while the reft 
of the body is white, but different from that of the 
neck, when it is of this colour. 
It fermetimes happens, that the part of the fnell 
which has been renewed is of a different colour. This 
apparent deviation will appear lefs difficult to be re- 
conciled to the explanation of the procefs which has 
now been given, if we attend to the circumftance that 
the new ffiell formed oppolite to the neck of the ani- 
mal is never different from that of the old ffiell, ex- 
cepting that the external furface is extremely rough, 
and prefents numerous furrows or grooves, in place of 
the fmoothnefs and fine polifh of the old ffiell. In this 
cafe, the inequality of furface is occafioned by the mo- 
tion of the animal retiring within its ffiell, before the 
new piece has acquired fufficient confiftency and folidi- 
ty ; and thus the new ffiell, having contracted on its 
furface wrinkles cr furrows, the light is very different- 
ly reflected. But there is another caufe for this dif- 
ference of colour in thefe circumftances. When a 
large piece of ffiell is removed, the firft layer which is 
formed is ufually white. The particles of the fluid 
which are neceffary for the formation of the ffiell of 
this colour, feem to be more eafily excreted from the 
furface of the body than the particles of fluid which 
go to the formation of any other colour. It is ob- 
ferved that the body of the animal is covered with this 
fluid, long before there is any appearance of fecretion 
about the neck. This fiquid is extended to the peck, 
and there produces a new layer of white ffiell ; but 
as this layer is extremely thin and tranfparent, it does 
not prevent the ufual fecretion of the colouring matter 
at the neck to appear. In this period of the procefs, 
if the animal retire within its {hell, the new layer, ft ill 
adhering in many points to its body, and not having 
acquired fufficient folidity, will be diflorted and wrink- 
led •, and not only exhibit that inequality of furface 
which generally appears in ffiells thus formed, but the 
arrangement of the ftripes or colours will alfo be de- 
ftroyed. 
It would be a very falfe conclufion from this account 
of the mode^of the formation of the ftripes which ap- 
pear on certain fpecies of ffiells, that the external fur- 
face of all ffiells ffiould be marked with colours, or 
ffiould be uniformly of the fame colour ; and that 
there ffiould be no {hells whofe external furface is 
marked with different fpots, differently arranged, of 
an irregular figure, and feparated from each other by 
unequal intervals. For if it has been ffiown, that 
thefe colours are produced on the furface of the ffiell, 
only by means of the fecretory organs, fituated on the 
neck of the animal, it cannot be fuppofed that the 
fume effefts will follow, unlefs the animal is placed in 
the fame circumftances. Thefe fecretory organs, there- 
fore, mult exift during the entire formation of the 
ffiell, to furniffi the fame quantity of colouring matter 
changes in during the whole of its progrefs. But if it happen, on 
t e organs, the contrary, that thefe organs undergo any change ; 
if the pores through which the liquid is poured out to 
form a ffiell or part of a ffiell of a brown colour, be- 
come too large or too fmall, or in other refpefts change 
their form, after having poured out a certain quantity 
of this fluid 5 and that thofe which furnifli the fluid of 
'which the white part of the ffiell is compofed, are alfo 
Caufes of 
this. 
93 
47 1 
changed, it muft happen that the (hell which is pro- Of the Con- 
duced is marked with different black and white fpots, p^Vts'Yf 
combined with a degree of irregularity correfponding c^ c u ? ^ c , 
to the change on the fecretory organs. This will ap- 
pear to be the cafe, by attending to the changes which 
take place in the fecretory organs of fnails which pro- 
duce coloured ffiells j for in them it may be obferved, 
that the colours are diftindt and well marked in fome, 
towards the opening, while they are fcarcely percepti- 
ble on the firft turn of the fp're towards the tip of the 
{hell ; and thefe changes of colour cannot be luppoted 
to exift; without a correfponding change on the fecretory - 
or g a , ns - . . . .94 
The fluidity of the liquid feoreted for the formation Difference 
of the ffiell, has probably alfo fome effedt in the regu- fluidity 
lar diftribution of the colours which appear on fome ‘ n 
fpecies. It is eafy to imagine that fome animals may £C j 
fecrete a fluid for the formation of the ffiell, of fuch a 
degree of fluidity as to flow eafily from one place to 
another, and thus produce irregular marks on the {hell. 
But beiides, if there are fecretory organs fituated on 
the neck of the animal, which prepare fluids of differ- * 
ent colours ; if the animal moves, or is difturbed by Motion of 
any means, when thefe fluids are excreted on the fur- the animal 
face, the colours will appear in a different place from during the 
their original diftribution, or be mixed and blended to-^^ e ‘ mat _ 
gether, and thus occafion that irregularity which is ob-ter, 
ferved in thofe parts of ffiells which have been la ft pro- 
duced, or renewed, ^ 
But it will be neceffary to have recourfe to the firft: Secretory 
of thefe caufes, namely to the change of ftrudture in organs en- 
the fecretory organs of the neck, to explain the regu- ' ar S e wlt *\ 
lar diftribution of the round fpots, or of thofe of a 1 * 16 aniir!a '' 
fquare or rectangular figure, with which certain {hells 
are marked, and to fuppofe that thofe veffels which are 
arranged in a fquare or rectangular manner, which 
furnifli peculiar fluids, are ffiut or open at different 
periods, ft may happen that the developement of a 
great part of the animal, occafioned by a more vigor- 
ous growth in certain fpecies than in others, may, in 
fome cafes, be the only caufe of thofe regular fpots, 
fometimes white on a coloured ground, and fometimes 
coloured on a white ground, which the {hell exhibits, 
if the glands which fecrete the colouring matter cor- 
refpond in their diftribution to that of the divifions on 
the ffiell, and if they occupy a greater fpace on the 
neck than is ufual in other fpecies. In this way may 
be accounted for, the regularity of thefe marks, and 
the increafe of their fize, which is ufually proportioned 
to that of the turns of the fpire, from the confederation 
of the fecretory organs of the animal enlarging in the 
fame proportion as the other parts of its body, and 
their effedts in the formation of the ffiell correfponding 
to the developement of thefe parts. Hence it follows, 1 
that the largelf marks are obferved on the external con- 
volutions of the ffiell. 
According to Reaumur, the laft layer of the ffiell Laft formed 
which is formed from a fluid fecreted from that part of ^ a )’ er l 7 u " 
the furface of the animal’s body which does not reach w “ ite ‘ 
the neck, ffiould be white, and this is moll generally 
the cafe. In thofe fnells which are internally colour- 
ed, the fluids fecreted from the body of the animal 
are of the fame colour, and they take the place cf 
thofe which are ufually white, or of a pearly nature, as 
is obferved in many others. The nature of thefe in- 
ternal 
