Now in three species of Lepas, in Dichelaspis Warwickii and in
Scalpellum Peronii, Darwin saw, on tearing recently-affixed animals from
their point or support, that a long narrow band issued from the same
point of the antennae; its end was torn away, and in Dichelaspis,
judging from its ragged appearance, it had attached itself firmly to the
support. From this it follows that this appendage in Lepas australis can
hardly be anything but a young cement-duct. If, therefore, the
supposition that the appendages on the antennae of the pupae of
Rhizocephala are young roots be correct, the roots of the Rhizocephala
are homologous with the cement-ducts of the Cirripedia. And this,
strange as it may appear at the first glance, seems to me scarcely
doubtful. It is true that the act of adhesion of the Rhizocephala has
never yet been observed, but it is more than probable that they attach
themselves, just like the Cirripedia, by means of the antennae, and that
therefore the points of attachment in the two groups indicate homologous
parts of the body. From the point of attachment in the Rhizocephala the
roots penetrate into the body of the host, whilst in the Cirripedia, the
cement-ducts issue from the same point. The roots are blind tubes,
ramified in different ways in different species. The cement-ducts in the
basis of the Balanidae likewise constitute a generally remarkably
complicated system of ramified tubes, with regard to the mode of
termination of which nothing certain has yet been made out.
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