rare. In the next higher class of the Gasteropoda, or univalve shells,
the sexes are either united or separate. But in the latter case the
males never possess special organs for finding, securing, or charming
the females, or for fighting with other males. As I am informed by Mr.
Gwyn Jeffreys, the sole external difference between the sexes consists
in the shell sometimes differing a little in form; for instance, the
shell of the male periwinkle (Littorina littorea) is narrower and has a
more elongated spire than that of the female. But differences of this
nature, it may be presumed, are directly connected with the act of
reproduction, or with the development of the ova.
The Gasteropoda, though capable of locomotion and furnished with
imperfect eyes, do not appear to be endowed with sufficient mental
powers for the members of the same sex to struggle together in rivalry,
and thus to acquire secondary sexual characters. Nevertheless with the
pulmoniferous gasteropods, or land-snails, the pairing is preceded by
courtship; for these animals, though hermaphrodites, are compelled by
their structure to pair together. Agassiz remarks, Quiconque a eu
l occasion d observer les amours des limacons, ne saurait mettre en
doute la seduction deployee dans les mouvements et les allures qui
preparent et accomplissent le double embrassement de ces
hermaphrodites. (2. De l Espece et de la Class. etc., 1869, p. 106.)
These animals appear also susceptible of some degree of permanent
attachment: an accurate observer, Mr. Lonsdale, informs me that he
placed a pair of land-snails, (Helix pomatia), one of which was weakly,
into a small and ill-provided garden. After a short time the strong and
healthy individual disappeared, and was traced by its track of slime
over a wall into an adjoining well-stocked garden. Mr. Lonsdale
concluded that it had deserted its sickly mate; but after an absence of
twenty-four hours it returned, and apparently communicated the result
of its successful exploration, for both then started along the same
track and disappeared over the wall.
Even in the highest class of the Mollusca, the Cephalopoda or
cuttle-fishes, in which the sexes are separate, secondary sexual
characters of the present kind do not, as far as I can discover, occur.
This is a surprising circumstance, as these animals possess
highly-developed sense-organs and have considerable mental powers, as
will be admitted by every one who has watched their artful endeavours
to escape from an enemy. (3. See, for instance, the account which I
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