Note the large stomach-cavity, surrounded by the digestive gland. Trace the convolutions of the alimentary canal through the foot to the anal exit. Note in the anterior portion of the foot a fused pair of ganglia similar to the visceral ganglia. These are the _pedal ganglia_, which are connected by a pair of delicate commissures, the _cerebro-pedal connectives_, with the cerebro-pleural ganglia. Note the glandular tissue which fills the cavity of the foot and surrounds the loops of the alimentary canal. This is the reproductive organ, which has its exit beneath the gills on each side of the foot. The sexes of the mussel are separate, but the reproductive organs are very similar. =Life-history and habits.=--The eggs (ova) of the female pass first into the supra-branchial chamber, whence, after being fertilized, they drop into the outer pair of gill-chambers. These outer gills serve as brood-pouches, and here it is that the embryonic stages are passed through. The embryo when ready to issue has a soft body enclosed in two triangular valves. At this stage it is called a _glochidium_. The glochidium on being discharged through the exhalant siphon of the parent falls to the bottom, where it remains for a time, when it attaches itself to some fish by the lower hook-like projections of the valves and leads a truly parasitic life for two months, after which it undergoes a metamorphosis and falls to the bottom again, there to begin an independent existence. Mussels often congregate in favorite mud or sand banks. Their food consists primarily of small organisms, both plants and animals, which are taken from the water entering the mantle-cavity. Mussels move about slowly over the muddy bottom of the stream by means of the muscular foot. OTHER MOLLUSCS.