Pvn H,i I'UitlS

92 PECTINIDJ2.
difficulty taken off. Notwithstanding this property, I
frequently find a small crab (Porcellana longicornis) in
their nests, and not unfrequently an annelid (Polynoe),
but almost invariably a greenish gelatinous annelid.
This last kind I have noticed lying across the tentacles
of a large Lima, which seemed to be quite at its ease
and by no means incommoded by its neighbour. I
have frequently kept L. hians in captivity for many
months. I have now (January 1863) one which I took
in May last, and it looks in good health. It com-
menced building in a day or two after it was put into
the tank, and has ever since lived under its own roof,
adding from time to time to the size of its oblong nest.
This word (' nest ') is, in a wide sense, not inappro-
priate as applied to the mode of architecture ; but it
must not lead to the idea of incubation, with which the
structure seems in no way connected." I am indebted
also to Mr. Robertson for another important observa-
tion,
viz. that he has seen some individuals of L. hians
shedding blood-red ova, and others spermatozoa at the
same time, and that the flow of ova continued for about
fifteen minutes, and to all appearance in two streams.
This observation is of great value as regards the generative
system of the Lamellibranch Mollusca; but we
must not overlook the possibility that each individual
may be of both sexes, although the period may vary for
the development of its — i. e. organs that it may be male
at one time and female at another, as is said to be the
case with Valvata and Ancylus among the freshwater
univalves. Or it may be analogous to what takes place
in certain flowering plants. Lobelia is hermaphrodite,
but usually sheds its pollen before the anther is prepared
to receive it, so that self-fertilization is seldom
effected, and the pollen of a neighbouring plant with the