342 Natural History of Molluscous Animals : 
lime from the cloak, and that then the growth of the shell 
goes on as usual, as is indicated by the plain intermediate 
spaces. We may further suppose, that, when the seminal tur- 
gescence has subsided, the fluids are couuieuea in greater abun- 
dane to the skin, wihemite an accumulation of calesaenit matter 
in the margins of the collar, and a co sequent varix or rib. 
We may minke such or similar suppositions, but they are idle 
and improbable ; and I mention the hypothesis rather from 
respect to its able author than from any the slightest convic- 
tion of its truth. It is inconsistent with analogy to believe 
that the Molltsca are influenced by the foal passion ere 
they have attained maturity, yet the ‘hypothesis supposes that 
some of them feel its power almost from the date of their 
birth, and afterwards at very short and frequent intervals ; 
while others, of the same genus even, are swayed by it at dis- 
tant periods, and only two or three times during the term of 
their existence. And in what predicament are those which 
are plain and ribless ? Are we to believe that their life is love 
unceasing or that it ceases only as the animal reaches ma- 
turity, and is about to finish the aperture of its edifice ? 
A theory of the formation of shells different from that just 
explained was once maintained by many naturalists, and 
amongst others by Klein and Bonnet, men of great learning 
and celebrity. They said, that the full-grown shell was a mere 
evolution of the foetal one, from the addition of matter by in- 
tusception ; and they supported the theory by the observation, 
that the shel! yet unborn has as many whorls as the adult. 
The observation is contrary to fact * ; and it is now generally 
admitted that the collar secretes the material of the building. 
« Tt is found to contain in its glands or vessels the canenete 
of lime in a free state; so that, when the surface of the collar 
is touched by any foreign body, at each point of contact a 
quantity of it is thrown out mixed with a tenacious mucilage. 
To be still further convinced of the fact,” says M. Gaspard, 
in an interesting essay on the phy siology of the Helix poma- 
tia, “ I cut off the collar of the mantle, and having thrown it 
into a dilute acid, a quantity of gas was given off, and the 
liquid gave the usual white precipitate with the addition of 
soda. ‘No other structure similarly treated afforded the same 
results.” + Further, if we drill a hole in the shell, the animal 
fills it up, not by any secretion from the adjacent portion of 
skin, but by withdrawi ing the collar as far as may be neces- 
* See the admirable preface to Muller’s Historia Vérmium, vol. ii. p. XXi. 
and xxiv. 
+ Zoological Journal, i, 96. 
