VOL 1] Variation in Shells. : 322 
shell has no inherent power of repair, then all repairs which are 
frequently performed on shells must be mechanical or constructive. 
In order to show how completely the shell is under the control of 
the will of the animal, I quote again from Woodward’s Manual of 
the Mollusca, pages 35-36: . 
_ “ The power which mollusks possess of dissolving portions of their 
own shell is exhibited by the murices in removing those spines from 
their whorls which interfere with their growth.”’ 
“The young cowry has a thin, sharp lip, which becomes coiled 
inwards and enormously thickened and toothed in the adult; 
the Teroceras develops its scorpion -like claws only when fully 
grown; and the land snails form a thickened lip or narrow their 
apertures with projecting processes, so that it is a marvel how they 
pass in and out and how they exclude their eggs. Yet at this time 
they would seem to require more space and accommodation in their 
houses than before, and there are several curious ways in which 
this is obtained. The Neritide and Auriculide dissolve all the 
internal spiral column of their shells, the cone removes all but a_ 
paper-like portien of its inner whorls; the cowry goes still further, 
and continues removing the internal layers of its shell wall, and 
depositing new layers externally by its overlapping mantle, until, 
in some cases, all resemblance to the young is lost in the adult.” 
I quote the following from Tryon’s Structural and Systematic 
Conchology, pages 31 and 32, which, it seems to me, is conclusive 
evidence that not only is the shell a construction, but that its forma- 
tion is an acquired habit: 
‘‘ The question of the parasitism of the animal of the Argonaut in 
its shell, originally assumed by distinguished naturalists, has been 
so long debated that quite a literature upon the subject has accumu- 
lated. The want of attachment of the animal by adductor muscles, 
and the fact that the shell itself is not moulded on the animal’s body 
and does not correspond to its shape, were considered such strong 
evidences of parasitism that the animal itself was described as 
Ocythe and the shell as Argonauta.” 
“The observations of Madame Jeanette Power first set this vexed 
question at rest by showing that the animal builds its shell by the 
exudation of material from the expanded velamentous arm of the 
female, instead of from the mantle, as in true shells.” 
The isan is born without a spcapipets) > shell; wane the — 
