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50 American Seashells
female also differs in having its two dorsal arms enlarged at the end to form
a veil or mold with which she secretes a shell. In a vast number of species,
the males are characterized by having one of the arms modified to form a
copulatory organ. This arm is known as the hectocotylus. In certain octo-
pods, including the Argonauta, this arm is broken off and left in the female
to fertilize the eggs. In all the other groups the hectocotylus is simply held
inside the female until copulation is complete. It is interesting to note that
more than 2000 years ago Aristotle recorded the presence of the hecto-
cotylus arm in the octopus and correctly associated it with its sexual purpose.
In the males the sperm is gathered into large sacs or spermatophores
of several inches in length. These sacs find their way in some unknown
manner into the hectocotylus arm. Each sac contains a tiny, coiled, spring-
like filament which spews the ripe sperm out of the sac.
The eggs of the cephalopods are laid in various ways. They may be
single and floating in the pelagic species, such as Oegopsida, congregated
together in a shelly nest as in Argonmita, laid in jelly tubes as in the Loligo
squid, or anchored in grape-like bunches under rock ledges as in the Octo-
pus. The embryo emerges from the tgg fully developed and does not have
a free veliger stage. With the aid of a lens it is possible to see the beautiful
splotches of bright chromatophores in the skin of the tiny young even before
they hatch. About a hundred eggs are laid at one sitting by the octopus;
the squid tgg strings from one female may contain over 40,000 eggs. Some
species of octopuses take pains to watch over their brood of eggs and from
time to time may carefully go over them with their tentacles to remove dirt.
THE CHn01