Plagiochæta sylvestris, Hutton, 1876 (= P. punctata, Benham, 1892).

In the year 1876 Captain Hutton^* gave a brief account of the external anatomy of several New Zealand earthworms, amongst which were two species which he placed in the genus Megascolex—viz., M. sylvestris and M. lineatus. In the year 1892 I gave a detailed account^† of the anatomy of a worm collected on Maungatua, for which it was necessary to create a new genus, and I termed it Plagiochœta punctata. At that time I was ignorant of Captain Hutton's article; but in 1892. Mr. Beddard^Dagger; suggested that in all probability M. sylvestris belonged to this new genus. This supposition was confirmed by me when, in 1898, I had the opportunity of examining Hutton's types,^§ preserved in the Otago University Museum, and in a note upon these types I pointed out that “it is difficult at present to determine whether M. sylvestris is or is not identical with P. punctata”; and I recognised that M. lineatus belonged to the same genus. A renewed examination of the type, and of other specimens collected in the neighbourhood of Dunedin, where the type was collected, has enabled me to establish this identity, and, further, to indicate the differences, external and internal, that exist between P. sylvestris and P. lineatus in a more detailed manner than was possible in my former note.

Habits.—P. sylvestris occurs in rotten logs in the remains of the bush country that forms the Town Belt around Dunedin, as well as on the slopes of Maungatua, and no doubt elsewhere. It is still pretty plentiful in our Town Belt, and I have found it especially in fallen Griselinia trees. The colour is chocolate, and closely resembles the vegetable mould—the digested wood—amongst which it lives. It is marked, as I noted in 1892, with white spots, in which the chætæ are inserted, while the nephridiopores are also indicated by still more conspicuous white spots, readily visible to the naked eye. The species is extremely active, and moves in a straight line with great rapidity, using its mouth as an organ of adhesion. It contracts its body to about half its length, then thrusts its head forward and extends itself fully; there is no wriggling or undulation of the body. When extended one specimen measured was 2 in. (50 mm.);

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when contracted, 1 3/16 in. (25.5 mm.). It appears to move backwards with almost the same ease with which it moves forwards.

But what is most remarkable is its ability to climb up a vertical surface. I placed a specimen in a clean dry glass beaker 4 in. in height. It climbed up this in a straight line, and dropped over the edge on to the table. Here it remained without a wriggle for a few seconds, in the same position as it fell. I noted that it moved even more rapidly vertically up this smooth glass than along the horizontal surface of the table. On holding the beaker in various positions, it nearly always took a vertical direction.

The worm, when slightly pinched with forceps, readily breaks into two pieces. It is not difficult to imagine the value of these habits in the struggle for existence. The negative geotaxis is, of course, of importance in gaining its normal habitat. Its ready autotomy probably protects it if perchance it is touched by a bird probing the log for grubs, &c.

Anatomy.—The two species, P. sylvestris and P. lineatus, agree closely with one another in external form and in certain structural characters, and differ in some of these respects from certain other species to be described below./Each is about 1 ½ in. to 2 in. in length, and contains from seventy to ninety segments. The body is relatively broad in proportion to the length, and is broadest in the middle.

The chœtœ are about fifty in number, set in couples,^* of which there are twelve or thirteen on each side. A distinct dorsal and ventral gap exists, the width of which in relation to the ordinary gap between couples is variable, being at least twice, or even thrice, the latter.

In my note of 1898 I laid some stress on the differences in the widths of these median gaps, but further comparison leads me to consider such differences as individual or even segmental variations.

The clitellum always covers segments 14 to 17, though the number of fully mature individuals available does not enable me to be certain as to any constant differences between the two species in this respect.

The porophores on 17th and 19th segments are set in a slight depression, capable of being converted into a narrow furrow on contraction, so that the porophores meet their fellows. This depression involves the ventral surface of segments 16 to 20. The porophores are in line with the lowest couple of chætæ; the male pore, on the 18th, is just outside this couple. There is no spermatic groove, such as

The penial chœtœ are especially diagnostic. Each is a long gently curved bristle practically smooth on its shaft, and terminated in a blunt point, which is not upturned.

The spermatheca is globular, with a short wide duct, into which opens a single tubular diverticulum, which invariably, as far as my observations on several individuals go, is præseptal.

P. lineatus, Hutton.

Hutton's original specimen was obtained at Queenstown, on Lake Wakatipu, in Otago. I have been able to examine other specimens, collected by Mr. Malcolm Thomson on Ben Lomond, a mountain 5,747 ft. in height overlooking the town. The differential characters are as follows:—

The prostomium is tanylobic—i.e., its prolongation completely cuts through the 1st segment, as Captain Hutton shows it in his fig. F (1876).

The clitellum appears to be limited to segments 14 to 17, and I have observed no copulatory tubercles; but in both of these characters I must for the present reserve judgment, owing to lack of sufficient material.

The dorsal vessel is single; and the hearts are in 10, 11, and 12.

There is a small gizzard in segment 6, recognisable on dissection.

The œsophageal gland is in segment 14, projecting slightly into the 13th segment.

There are only three pairs of sperm-sacs, in segments 9, 11, and 12.

The penial chœtœ are longer and more delicate than in P. sylvestris, and the tip is bent upwards and slightly excavated, so as to be spoon-shaped, though in side view the tip is pointed. But, further, the shaft is marked by numerous distinct but fine, interruptedly transverse, low ridges, finely serrated.

The spermatheca is ovoid, with a short and comparatively narrow duct, into which there open two short and somewhat globular diverticula, the lower of which is præseptal. One of these diverticula—perhaps both—is lobed—i.e., its free extremity is notched by one or two furrows. In the type it is the lower which is thus notched; in the Ben Lomond specimen it is the upper one.

These two characters—the penial chætæ and the sperma-thecæ—are very definite differential features of these closely similar species.

Plagiochæta lateralis, n. sp.

Locality.—The shore of Lake Thompson, 1,100 ft. above-sea-level, on the track from Lake Te Anau to George Sound. Collected by Mr. J. Mackenzie.

Colour.—Pale-greyish, with dark-brown clitellum.

Dimensions.—The longest of the dozen specimens measures 55 mm., with a diameter of 5 mm. The body is rather depressed, with a slight groove along the median dorsal and ventral surfaces. The number of segments is 100.

The prostomium is half epilobic, with a transverse furrow before the end of the longitudinal furrows.

The chœtœ are twenty-four (about) in each segment. They are not in couples, but are arranged in two groups on each side, an upper and a lower, separated by a distinct lateral gap, which peculiarity suggested the specific name. The lower group consists of five chætæ, the upper group of seven chætæ; the latter are further apart than the former. The dorsal gap is greater than the ventral, and each is greater than the lateral. The arrangement may be represented by the following formula, in which the vertical lines represent chætæ and the numerals indicate the relative distances, as measured by an eye-piece micrometer on the flattened skin. V, L, and D are the ventral, lateral, and dorsal gaps respectively.

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9 | 2 ½ | 2 | 2 ½ | 2 ½ | 5 ½ | 3 | 3 | 4 | 4 | 3 | 4 | 12.

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V a b c d e L f g h i j k l D

No doubt the actual distances vary, not only in specimens, but in different parts of the body.

The clitellum covers segments 14 to 17 inclusive; it does not extend over the ventral surface, but ceases at about the level of the porophores.

Genital Pores, &c.—The porophores are feebly developed on 17 and 19, and are in line with about chæta e—i.e., almost laterally placed. There are four chætæ below each, and four chætæ below the male pore in 18th segment; and sections show a 5th chæta close to the pore in each of these segments. These chætæ are further apart on these segments than elsewhere. There is a distinct and curved spermatic groove, convex outwards. In some of the specimens copulatory tubercles exist, but asymmetrically on the right or left of segments 18 or 20. In none are they fully developed, when, no doubt, they will be paired.

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The oviducal pores are in line with the gap b/c, the spermathecal pores between ⅞, 8/9, in line with the chætal gap e/f; and in several of the individuals there is a pair of pitted tubercles on the 8th segment, just behind the chætal ring, in line with the gap d/e.

transversely ovate, and the duct is scarcely distinguishable on dissection, but receives right and left a small ovate diverticulum with a long narrow duct.

Plagiochæta rossii, n. sp.

Locality.—Five specimens were collected in the bush on the shore of Lake Te Anau in 1900. I name this species after the collector, Mr. Donald Ross.

The colour, in formol, is purplish-brown, with a darker-brown median dorsal stripe. The preclitellar region is greyish-brown.

Dimensions.—The mature individuals vary from 105 mm. to 165 mm. in the preserved condition. In a specimen measuring 158 mm. its greatest diameter is 7 mm. at segment 8, and also behind the clitellum. The preclitellar region is 20 mm. and the clitellum 11 mm. in length. This worm consists of 112 segments.

The prostomium is epilobic (three-quarters), without a posterior groove.

The chœtœ are about thirty-two to thirty-six in each segment, not in couples. Each chæta is implanted in a light spot. There is no perceptible diminution anteriorly, for I count thirty-two on the 7th segment and thirty-four on the 3rd segment. There are small ventral and dorsal gaps, but no lateral gap, the series of sixteen or eighteen chætæ on each side being practically equidistant.

The clitellum extends from 13th to 17th segment, and in the largest individual the 18th segment differs in colour from the 19th, and looks as if it, too, would become part of the clitellum. The organ is continuous ventrally in its anterior region, but on segments 16 to 20 is a white transversely oval genital area, containing the genital pores.

Genital Pores.—The porophores are prominent. There is no true spermatic groove, but a ridge passes from 17th to 19th segment on each side, having a rather peculiar arrangement. Starting from the 17th porophore, the ridge curves down the posterior face with an outward sweep and reaches the inter-segmental furrow, where it disappears. A similar ridge occurs on the anterior face of the porophore on the 19th segment. Then in the 18th is a curved ridge, convex outwards, connecting the two other ridges. The ridge is a rounded prominent structure, forming the outer boundary of an indistinct furrow whose inner boundary is formed by the glandular tissue of the body. This ridge seems to contrast with the definite groove found in many Acanthodrilids, for in them the groove is the conspicuous structure; here, in Plagiochœta, it is the external (and only) ridge that catches the eye. How far we may distinguish these two things is uncertain, but the

The dorsal vessel is distinctly double, right up to the pharyngeal region. The last heart is in segment 13.

The Alimentary System.—The gizzard is elongated, but wholly confined to segment 6. There is a large œsophageal gland in segment 12, behind which the gut is noticeably reduced in size—not only in breadth but also in length—owing to the reduction of the segmental cavities already referred to. It does not commence to dilate till the 18th segment to form the intestine.

The worm is micronephric, the tufts of tubules being concentrated near the nerve-cord. I have been unable to trace the nephridium to the surface, but there are well-developed funnels.

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Reproductive System.—The position of the gonads is altogether unique. Both testes and ovaries are situated not on the septa bounding the segments, but on the floor of the body. Each testis is elongated in a direction parallel with the long axis of the body, and extends backwards to the posterior wall, terminating below the corresponding funnel. In the case of the ovary the same arrangement obtains; but the cavity of the 13th segment is greatly reduced, except below the ventral vessel, where the septum 13/14 is pouched backwards to form a tunnel-like pocket, which reaches nearly as far as septum 14/15. It is on the floor of this pocket that the two ovaries are placed; and, as the funnel of the oviduct is carried forwards by the overarching septum, the ovary comes to lie underneath the lip of the funnel.

Diagrammatic longitudinal section through segments 13 and 14.

a, gut; b, septum; c, ventral blood-vessel; d, body-wall; e, oviduct; f, ovary.

There are four pairs of sperm-sacs in the usual segments. The spermiducal glands are somewhat flattened and undulating.

There are no penial chætæ, but “transverse muscles” occupy segment 18.

Each of the spermathecæ (in segments 8 and 9) is a subconicál sac, with short duct, and around the latter is a nearly