25 
pass upwards and outwards in a slanting direction, to be inserted 
in the valve at the anterior and more dorsal portion of the im- 
pression of the posterior adductors. The divergence of these two 
large muscles forms a furrow in which a great part of the body, the 
heart, and large vessels, are lodged. A difference of opinion seems 
to exist as to whether a mussel can move. It may have the power 
to do so the fraction of an inch by the help of its byssus; but from 
the firm manner in which they are matted together by hundreds, 
and attached to sea-weed, gravel, and broken shell, it is more 
probable that they are firmly fixed, or rather permanently fixed, but 
not to the same extent as the oyster. Mr. Buckland says that if a 
mussel be packed close to the glass of an aquarium, a large, finger- 
like organ, the foot, will soon be observed protruding from the 
gaping shell, and applied to the surface of the glass. A small slit 
near the tip of the foot is then opened, and the end of the thread 
attached. The foot being withdrawn, the byssus will be seen lead- 
ing from it to the glass. At first this is apparently soft, but it 
hardens by contact with the water. The byssus is secreted by a 
gland at the base of the foot, and moulded in a groove which runs 
along the posterior side of the foot. At the tip is a fossa, capable 
of holding a certain quantity of the plastic material which forms the 
thread ; behind the gland of the byssus the muscular structure of 
the foot passes backwards in a falciform shape, the point of which is 
attached to the under surface of the adductor, between the ganglions 
of the branchial nerves. Behind the byssus, from this portion of 
tho foot, the generative orifice opens and discharges the ova into the 
branchial chamber. The mantle or cloak covers all the organs, ex- 
cept the adductor muscles which run through it from one shell to 
the other ; it is open the whole length of the ventral and posterior 
inferior border of the shell, as far as the back part of the posterior 
adductor. With reference to the digestive system, the mouth termi- 
nates in a short esophagus, soon leading into a stomach. This is 
simply a dilation, irregular in shape and surrounded by a liver of a 
pale green colour and spongy texture. The liver discharges its 
secretions into the stomach by several ducts. The intestine 
describes several turns throughout the substance of the liver. The 
first turn is to the left. It then curves downwards, the concavity of 
the turn looking towards the foot, called the ‘neural flexure” by 
Huxley. After crossing and recrossing itself, it terminates in the 
straight portion or rectum, which emerges from the liver, and pass- 
ing through the heart, covered by the pericardium and ventricle, 
terminates in the upper of the two pallial chambers at the back of 
the posterior adductor. The stomach and alimentary canal contain 
the skeletons of animaleules and diatomacee, also the larve of a spe- 
cies of entozoa. The relation of these larve to the mussel and cockle 
has lately been discussed by the Quekett Microscopical Club, (see 
papers by D. Moore, M.D., and W. Fells Wood, in the Journal of 
