ranean: thus, Tomopteris onisciformis and T. Scolopendra are most probably distinct species. Mr. Gosse's Johnstonella Catharina is, no doubt, a synonym of the latter, since Mr. R. Ball records that Bryarea Scolopendra has been taken in Dublin Bay by Dr. Corrigan (Report Brit. Assoc. 1849, p. 72).”—Gray, Ann. & Mag. Nat. Hist.

The Nereis phasma of Dalyell (Pow. Creat. ii. 260. pl. 36. f. 16, 17, & 11) is a second species, apparently, of this singular and beautiful genus. Sir John procured his specimens in the Firth of Forth at Newhaven, and on the Isle of May; and he thus describes the animal :-"This animal is towards an inch in length. It might be inscribed in a triangle. The head is forked or cleft, furnished with two long antennæ issuing from the sides, between the roots of which, or somewhat behind them, are two black eyes, rather oval, and probably compound. If the body is divided into segments, they are invisible from transparence. If so, the segments consist of a central portion, as the central part of the Nereis, and a long arm, an integral part towards each side, gradually shortening from the middle to the lower extremity, which is pointed. Towards this extremity they degenerate into mere stumps, which seem to be successively developed as arms. Sixteen or seventeen of these arms were conspicuous in (one example), and fourteen or fifteen in (another). In some others were four or five or seven pair of limbs or arms. The extremity of the limb is cleft, and terminates in two portions like hollow walnut shells. To some of the artists the termination seemed a pencil. An intestinal organ traverses the whole length of the body.

"This animal is absolutely colourless; it can be distinguished from the water only when in particular positions, and under a particular incidence of the light. It swims horizontally, and then partly by faint undulations. In this position the greater convexity of the back, and slighter convexity of the belly, are sensible. It always seeks the higher part of the water, near the surface, like the Medusa, keeping the antennæ recurved. I sometimes believed that segments were indicated on the under surface; that the whole was crossed by wrinkles which were effaced on extension; and one of the cleft extremities of the limb also seemed to move as if by a joint; and the hollows of some contained a minute yellow body like an The animal is rather of a gelatinous appearance. It can be preserved with difficulty, from being liable to entangle itself in every foreign substance, and is easily mutilated in its struggles for liberation."-Dalyell.

ovum.

Order VI. ANNELIDES.

CHETOPODES (-), Blainv. Princip. d'Anat. Comp. i. tab. 7. sp. 177. ANNELIDES, De Quatrefages in Ann. des Sc. nat. viii. 99 (1847). ANNULATA APPENDICULATA POLYCHAETA, Grube, Fam. Annel. 26. Char. Worms segmented, the segments forming a section of a cylinder or semicylinder, and furnished on each side with prominent lobular or wart-like feet armed with many retractile bristles of various kinds, in one, two, or three fascicles: head either distinct with organs of sense, or indistinctly defined with tentacular filaments on its crown or sides: branchiæ variously attached, usually combined with the feet, filamentary, foliaceous, or arbuscular, rarely obsolete or cutaneous: anus opposite to the mouth, terminal, and usually protected with styles or lobules. Blood red or green, circulating in close vessels: respiration aquatic: zoophagous or geodephagous: the sexes separate or united in the same individual: marine or littoral.

It may be useful to give a brief explanation of the nomenclature employed.

The BODY is the entire worm. The form is defined by familiar words, in general used in their common acceptation, but it is convenient to call it lumbriciform, when it is nearly cylindrical, like the Earth-worm; scolopendriform, when it is flattened on both dorsal and ventral surfaces with nearly parallel sides, like the Centipede; and eruciform, when it is thickish in proportion to its length, and grub-like. The body is formed of a specific number of SEGMENTS developed in longitudinal succession, and divided from each other by a plain suture. They are annular; and subdivided sometimes into rings by circular folds of the skin.

The SEGMENTS are similar when they resemble each other in structure generally; and they are dissimilar when some vary from the others in any addition, or abstraction of organs.

The Segments are of three kinds more or less distinctly marked, -the cephalic,-the thoracic,-and the abdominal.

The Cephalic is that portion of the body anterior to the first transverse suture. It may be composed of three or more segments in a more or less intimate union, but the demonstration, however useful in theoretical, is useless in descriptive anatomy.

When the aspect of the cephalic portion is such that we cannot call it otherwise than a head, the worm is said to be cephalous (No. IV. fig. 8); when it differs little from the other segments behind, and appears almost a continuation of them, it is subcephalous (figs. 9, 11); and when there is no appearance of a head, and the front terminates abruptly, the worm is acephalous (fig. 10).

The HEAD (fig. 8) has various appendages. There are usually one or two pairs of eyes placed on the dorsal aspect behind the

antennæ. In the subcephalous and acephalous tribes eyes are generally absent. They are always sessile, simple, and immoveable.

Antenna (figs. 8 a & 11 a) exist only in cephalous genera. They are soft, setaceous filaments, varying in number from one to five, and distinguished from the other appendages by arising directly from the head. They are usually jointed at the base, and are not retractile.

Palpi (fig. 8 p) are seldom found. They are also soft filaments, entire or jointed, and originate externally from the sides of the oral orifice. Tentacula (figs. 8t & 9 t) are the soft setaceous or filiform nonretractile processes which arise from each side of the cephalic segments in pairs, and spread laterally. They are sometimes jointed; often very long, and remarkably contractile in the acephalous genera.

The Mouth (fig. 11 m) is underneath the head, and is a round or transverse entrance to the oesophagus and intestinal canal. It has usually a plain margin. In the acephalous genera it is terminal and emaxillary, but occasionally furnished with external tentacles. In the subcephalous it is subterminal or ventral; and in the cephalous nearly terminal, looking forwards horizontally.

The Mouth in the cephalous tribe is almost always furnished with

a Proboscis, viz. the œsophagus, or upper portion of the intestinal canal, in a state of protrusion. It consists of one or two segments, and is evolved at pleasure by a process of evagination. It is often armed with horny jaws in opposite pairs; sometimes roughened on the surface with horny prickles; sometimes villose with soft papillæ ; sometimes encircled at the orifice with soft papillæ or short tentacles; and sometimes plain. These modifications of the organ afford important characters in classification.

The Thoracic Segments immediately succeed the cephalic or head. In the cephalous genera there is only one thoracic segment (fig. 8th); as is also the case in many of the subcephalous. From its position, I usually describe it as the post-occipital,-a name to be preferred as implying no theory. It is remarkable for being naked,—that is, it has no soft appendages or setigerous feet, and constitutes, sometimes, a sort of neck.

In the acephalous genera, and less markedly in some others, the thoracic segments are distinguished by peculiarities in their structure and appendages;-they are more fleshy and contain the primary organs of life; and to them the Branchiæ (fig. 106) are limited in many genera. They are readily enough defined.

The Abdominal Segments follow the thoracic and complete the body. They are more numerous than the cephalic and thoracic combined, more uniformly alike in their appendages, and liable to vary in their number, so that, as a character, number is here of no value, excepting in a few instances. They gradually lessen in size as they approach the posterior extremity; and the last segment is called the anal. This has no setigerous feet, often no soft appendages, but more commonly a pair of soft filaments, called styles, project behind; or a series of short papillæ surround the vent, which is terminal and central.

The Segments are furnished with various appendages, which are precisely similar on each side, but modified more or less on different segments. Of these appendages the Foot is the principal, and with it the others are commonly combined.

The Foot is a papillary projection on the side of the segment for the insertion of the bristles. It also affords, in most worms, a basis of attachment to the Branchiæ, and certain soft setaceous filaments called Cirri or tentacular cirri.

The BRANCHIE are the breathing organs. In the cephalous and subcephalous families they are attached to the base of the foot on the upper or dorsal side, either restricted to a certain number of segments, or found on all of them. They vary much in form. They are either arbuscular, or semipectinate, or flat and veined, when their function is indisputable; or they are filamentary, or squamous, or lobe-like, or merely tubercular, when the ascription of the function becomes arbitrary, or a deduction from the theory of homologies and degradation of organism. In many acephalous genera the Branchiæ are placed on the crown in beautiful tufts (fig. 10); and in all acephalous worms the function of the organs is never doubtful. They often combine a tactile with the respiratory office.

The Cirri are the tentacula of the body; and we may call them,

b

No. V.

in some genera, tentacular cirri from their similarity to the tentacula on the sides of the head. They are simple, soft, tapered filaments or papillary processes attached to the dorsal and ventral lobes of the foot, at or near the base. Their office appears to be tactile. The Foot, properly so-called, is the papillary process, tubercle, or fold in which the Bristles are sheathed. When the process is single and undivided, the foot is said to be uniramous; when it is divided into two lobes, it is biramous (No. V. fig. 12). The upper division is called the dorsal branch, and the inferior the ventral branch. They are more or less apart, sometimes so near as to coalesce, and not to be distinguished from the uniramous excepting by the presence of two bundles of bristles,-sometimes so wide asunder that they seem to have no connexion. latter the foot of the Nephthys is a good example (fig. 12). In this figure dfis the dorsal branch, and of the ventral branch armed with their long bristles; I are the

Of the

of

12

br

compressed lamellæ attached to the foot; br are presumed to be the branchiæ; and c is the inferior cirrus; and, in this species (N. longisetosa), there is no superior cirrus. This interpretation of the organs appears to me erroneous. The function of the sickle-shaped process is entirely conjectural; and surely the compressed lamellæ are branchial, although undoubtedly the function is not confined to them.

Bristles.-There are four kinds of bristles connected with the feet, viz. the Spine, the Spinet, the Bristles properly so called, and the Hooklets. Other bristles which belong to the body will be noticed under the genera in which they occur.

1. The Spine (Plate III. fig. 1) is subulate and straight, tapering insensibly from the base to the point. It is always associated with the bristles, there being one, or at most two, in the centre of each fascicle; and it is readily distinguished by being stouter and darkcoloured. It is not protrusile. Audouin and Milne-Edwards say that the base is placed in the bowl of a little cup; but certainly this is not usually the case. The basal portion is lighter-coloured than the upper.

2. The Spinet is not in general so stout as the spine, neither is it dark-coloured. It is found only on a few feet in some genera, and in most is absent. It is associated with the bristles, and is known by being stiffer and stouter, and different in shape. The apex is forcipate (Pl. III. fig. 2), or forked (figs. 3, 3*, 4, 5).

3. The Bristles are simple or compound.

The simple Bristle is formed of a single continuous piece. It is always fasciculate. It varies much in strength and size and figure;