OLIGOCH.,ETA, an order of annelids, of which the common earth-worm is a good example. Their locomotive appendages are in the form hf bristles attached in rows to the sides and ventral surface of the body ; no bra nchias; nil hermaphrodite; young pass through no metamorphosis. The order is divided into two families, terricora3 or earth worms, and limieeke or mud-worms and water-worms. These families have also been named, respectively. and aaidcs. In the /umbricus or common eart h-worm (q.v.), the edentulous mouth opens by n muscular pharynx and short Tophagua to a muscular crop or pro-ventrieulus; ut.ceeded by a second muscular stotiaten giziard. Salivary glands open into the pharynx, and other digestive glands open into the gullet. The perivisceral cavity is lined by a cellular membrane, which is continuous with a yellow cellular layer covering the intestine and large vessels, and which casts off its cells into the perivisceral fluid The blood circulating in the pseudo-hemal system is non-corpus ciliated, although red, while that contained in the body cavity is colorless, but corpuscles. In all the oligoeheeta the segmental organs communicate with the perivis
ceral cavity, and also externally with the outer medium. The most common example of the naidte is the tubifex rivulonam, found in the mud of ponds and streams. It is 1 or in. long and of a bright red color. The psendo-hemal system is provided with two con. tractile cavities or hearts, and a system of tames similar to that in the earth-worm, and also a system of lateral tubes opening externally. The reproduction is both non-sexual and sexual. Before maturity the young muffs throws out a bud between two rings, at a point generally near the middle of the body, and the strange phenomenon of this bud develop ing in'o a new individual, as well as each of the two parts of the parent on either side of this point, takes place. That portion of the parent in front of the bud develops a tail, whilst the portion behind the bud develops a head. Besides their non-sexual reproduc tion the =kite after going through a metamorphosis attain sexual reproduction.