


A STROLL BY THE SEA-SIDE. 243 
for cunners, or perch, and the fingers become stained a deep 
purple after handling the crushed animals. 
In the crevices. of the rocks, and in certain pools left by 
the tide, we shall find the common salt-water mussel (Plate 
6, fig. 10) closely compacted in great numbers. On attempt- 
ing to detach a specimen from the rocks, it is found that they 
are held in place by a strand of little silken threads, issuing 
between the valves of the shell, and adhering strongly to the 
rock. This bunch of threads is called the byssus, and a 
tropical genus, called Pinna, produces a byssus of consider- 
able size. Gloves have been woven from the fibres compos- 
ing it. The individuals covered by water display at the free 
end of the shell and between the valves (each shell of a bi- 
valve is termed a valve, hence the name bivalve, two valves), 
Which are partly open, two openings formed by the mantle. 
se openings are scarcely divided; one opening reaching 
hearly to the byssus is beautifully fringed with little arbores- 
cent fringes, the other opening is plain. If we watch the 
particles floating near these openings, it will be seen that a 
current of water is passing in at the fringed opening, while 
from the simple opening a current of water is as constantly 
‘sting. These currents of water are produced by the vibra- 
Gon of little moving hairs, or cilia, which line the mem- 
branes within. The gills, of which the animal has four, two 
on each side, are particularly covered by the cilia, so that if 
the Shell is broken open, and a piece of the gill is separated 
om the animal, it will swim round in the water like an 
independent animal for some time. We become acquainted 
With an excellent provision in this arrangement, for in the 
: Place the currents of water kept up in this way bring @ 
continual supply of fresh sea-water to the gills, and in the 
rond Place ‘the food of the mussel, which is mostly of an 
ufusorial character, is brought to the mouth by the same 
means. The two short openings we have seen in the mussel, 
: — genera like the clam are prolonged into two long 
a nn by one sheath, or form two distinct tubes as 
in other genera. 


