produced into a
tube nearly as long as the fish itself; this acts as an ovipositor by
means of which the comparatively few and large eggs (3 millimetres in
diameter) are introduced through the gaping valves between the branchiae
of pond mussels (_Unio_ and _Anodonta_), where, after being inseminated,
they undergo their development, the fry leaving their host about a month
later. The mollusc reciprocates by throwing off its embryos on the
parent fish, in the skin of which they remain encysted for some time,
the period of reproduction of the fish and the mussel coinciding.

BITTERN, a genus of wading birds, belonging to the family _Ardeidae_,
comprising several species closely allied to the herons, from which they
differ chiefly in their shorter neck, the back of which is covered with
down, and the front with long feathers, which can be raised at pleasure.
They are solitary birds, frequenting countries possessing extensive
swamps and marshy grounds, remaining at rest by day, concealed among the
reeds and bushes of their haunts, and seeking their food, which consists
of fish, reptiles, insects and small quadrupeds, in the twilight. The
common bittern (_Botaurus stellaris_) is nearly as large as the heron,
and is widely distributed over the eastern hemisphere. Formerly it was
common in Britain, but extensive drainage and persecution have greatly
dimished its numbers and it is now only an uncertain visitor. Not a
winter passes without its appearing in some numbers, when its uncommon
aspect, its large size, and beautifully pencilled plumage cause it to be
regarded as a great prize by the lucky gun-bearer to whom it falls a
victim. Its value as a delicacy for the table, once so highly esteemed,
has long vanished. The old fable of this bird inserting its beak into a
reed or plunging it into the ground, and so causing the booming sound
with which its name will always be associated, is also exploded, and
nowadays indeed so few people in Britain have ever heard its loud and
awful voice, which seems to be uttered only in the breeding-season, and
is therefore unknown in a country where it no longer breeds, that
incredulity as to its booming at all has in some quarters succeeded the
old belief in this as in other reputed peculiarities of the species. The
bittern in the days of falconry was strictly preserved, and afforded
excellent sport. It sits crouching on the ground during the day, with
its bill pointing in the air, a positi