Subclass

SUBCLASS II.—Enopla. Proboscis usually armed with one or several stylets. Muscle-layers two; an outer circular and an inner longitudinal layer. Nerve-cords internal to the musculature.

Order 3.—Malacobdellidea. Body short, with a sucker at the posterior end. Proboscis unarmed, opening with the mouth. In testine coiled, without pouches. This order contains the leech-like form Malacobdella, which lives as a parasite or commensal within the mantle-cavity of marine lamellibranch molluscs.

Order 4.—Hoplonemertidea. Proboscis armed. Intestine straight, with a blind, ventral, anterior diverticulum and paired lateral pouches.

Suborder I—Polystilifera. Stylet-base crescent-shaped, bear ing several stylets along its convex side. This suborder has been divided into two "tribes," the Pelagonemertoidae and Drepanophoroidae. The former consists of pelagic forms, in which cephalic and excretory organs and an oesophagus are absent, and the male gonads are confined to the anterior region.

This tribe is further subdivided into ten families (Nectonemer tidae, Pelagonemertidae, etc.). The Drepanophoroidae are bot tom-living forms in which cephalic and excretory organs and an oesophagus are present, and the gonads extend to the pos terior end. This tribe contains the families Alboganemertidae, Uniporidae, and Drepanophoridae.

Suborder 2.-Monostilif era. Stylet-base shaped like the handle of an awl, and bearing a single terminal stylet. This suborder contains five families, of which the best known are the Amphiporidae and the Prostomatidae.

Development and Life-History.

Some nemertines go through a remarkable metamorphosis. In Cerebratulus there is a curious free-swimming, ciliated larval stage known as the pili dium, which resembles a helmet with side lobes like ear-lappets, and with an apical "spike" of long cilia. The pilidium is pro vided with an alimentary tract which is destined to become that of the fully-formed larva. Two pairs of invaginations grow in wards from the outer covering so as to surround the intestine, and ultimately form the skin and muscular body-wall of the animal. The worm is thus developed within the pilidium, which is a mere temporary envelope. It finally becomes ciliated, escapes from the pilidium, and grows into an adult. In Lineus there is a creeping larval form known as the "larva of Desor." This has a ciliated envelope corresponding to the pilidium, within which the body of the worm is formed in a similar manner, and which is finally shed. In other forms the development is simple and direct, the pilidium stage being apparently suppressed.

The majority of nemertines live in comparatively shallow water, under stones or among algae and corals, in empty shells, or buried in mud or sand, where they frequently line their bur rows with a gelatinous tube. Certain species live as commensals

or possibly as parasites of other animals (crustaceans, ascidians, and molluscs). Nemertines usually progress rather slowly by crawling, though some are able to swim actively with an undu lating motion. They are carnivorous and extremely voracious animals, capturing their prey with the aid of the proboscis, and being able, in many cases, to engulf creatures of considerable size, the mouth being capable of great distension.

The eggs of some species are laid in strings or masses, em bedded in a gelatinous secretion. This appears to serve both as a protective covering and as food material for the larvae after hatching. In some species the female secretes a definite parch ment-like "cocoon" round herself before depositing her eggs. This cocoon is usually attached to a stone or weed. The body of the mother may even disintegrate after the deposition of the eggs, and form a food-supply for the young within the cocoon.

The body of many nemertines is capable of extreme extension and contraction. One common species of Lineus is often many yards in length when lying fully extended on a muddy bottom, and has earned the popular names of "bootlaces" and "india rubber-worm." Another peculiarity of the group is the readiness with which many species will break themselves up into innumer able short fragments under the stimulus of any sudden irritation. Such fragments are often capable of living independently for some time, and lost portions are quickly regenerated, some or all of the pieces developing into complete worms. The proboscis, if broken off, is likewise generally reproduced. (H. A. B.) NEMESIANUS, MARCUS AURELIUS OLYMPIUS, Roman poet, a native of Carthage, flourished about A.D. 283. He was a popular poet at the court of the Roman emperor Carus (Vopiscus, Carus, i). He wrote poems on the arts of fishing (Halieutica), aquatics (Nautica) and hunting (Cynegetica), but only a fragment of the last, 325 hexameter lines, has been preserved. It is neatly expressed in good Latin, and was used as a school text-book in the 9th century. Four eclogues, formerly attributed to Titus Calpurnius (q.v.) Siculus, are now generally considered to be by Nemesianus, and the Praise of Hercules, generally printed in Claudian's works, may be by him.

Complete edition of the works attributed to him in E. Bahrens, Poetae Latini Minores, iii. 0880 and J. P. Postgate's Corpus Poetarum Latinorum, ii. ; see also L. Cisorio, Studio sulle Egloghe di N. (1895) and Dell' imitazione nelle Egloghe di N. (1896) ; and M. Haupt, De Carminibus Bucolicis Calpurnii et N. (1853) , the chief treatise on the subject.