4 Transactions of the South African Philosophical Society. 
layers of the epidermis in which it was formed originally, one 
should either find that the base of the shell had penetrated into the 
skin to that extent, viz., 44 inches below the epidermis, or, as this 
is not the case, ‘‘ that the epidermis of the whale had ceased being 
formed under these specumens, whilst it had gone on being formed 
around and between them, to the thickness of four or five inches, and 
that it had subsequently disintegrated to this same thickness on its 
outer side, which processes would account for the summit of the shell 
being still on nearly a level with the surface of the whale.’ Darwin 
adds that he cannot believe this to have taken place, and continues: 
“‘The view which seems to me most probable is, that the rapid 
downward growth of the shell, besides indenting the whale’s skin, 
at the same time slowly pushes the whole shell out of the skin, and 
thus continually exposes the summit to the wear and breakage 
which seems to be necessary for its existence. On this view, the 
very peculiar form of T'wbicinella, which is retained during life, 
namely, the slightly greater width at top than at bottom is beauti- 
fully explained, viz., for the sake of facilitating the protrusion of the 
shell; for the ordinary conical shape of senile cirripedes, with the | 
apex upwards, would have rendered the pushing out of an imbedded 
shell almost impossible ; on the other hand, we can see that the 
likewise very peculiar, concentric, prominent belts may be necessary 
to prevent too easy protrusion.” 
If one remembers that the tubular shell rests with its lower edge 
on the soft inner skin, the corium, and that its basal surface is not 
closed with any hard substance, but simply with a membranous 
diaphragm, while the sides of the shell are provided with such 
prominent ridges it is difficult to imagine that it could be pushed 
out of the epidermis in this way. In fact, having removed a number 
of living specimens from the skin in which they were imbedded, I 
consider this pushing out as impossible. The skin around each 
shell is quite indurated, the ridges of the shell have their upper 
edge slightly turned upwards, and the shells adhere so firmly to the 
skin that one has to use considerable force in order to break them 
out even after splitting the surrounding body of skin lengthways. 
The observation, however, which I have made, enables us to 
understand the actual process. We saw that the larve of the 
cirripedes attach themselves to their permanent support by means 
of a cementing apparatus. Such a cementing arrangement appears 
quite sufficient for those species which live on rocks, shells, wood, 
or any other dead material, but it is evidently quite insufficient to 
account for their permanent adherence to the live skin of an animal. 
Supposing even they succeeded in attaching themselves, they would 
