Art. VII.—An Account of Acanthodrilus uliginosus, Hutton.
[Read before the Otago Institute, 13th November, 1900.]
In my “Re-examination of Hutton's Types of New Zealand Earthworms” (1) I mentioned the fact that I had been unable to find the “type” of “L. uliginosus.”† Since that date,
[Footnote] † Trans. N.Z. Inst., vol. xxxi., Art. xix.
however, Captain Hutton has been good enough to send me the type specimen from Christchurch, with the note that “it was collected many years ago in the swamp on which the town of Caversham now stands.” The specimen, when it came into my hands, was fairly well preserved, but naturally had lost all colour. It measures 6 in. by ⅜in., and consists of 145 segments. In other respects—and allowing, of course, for misinterpretation of the terms “male genital openings” and “vulvæ”—the worm agrees with Hutton's description (2). A careful examination of its external characters and of its internal anatomy enables me to state that it is identical with the worm to which Beddard(3) in 1885 gave the name Acanthodrilus novæ-zealandiæ, a name which henceforth will have to disappear from literature.
A few years ago the genus to which most of our endemic earthworms belong was called “Acanthodrilus,” but as the number of species has increased, and as these have been submitted to more and more careful scrutiny, it has been deemed necessary to subdivide the genus. Thus, Bed-dard(4) established the genus Octochætus in 1892 for a group of species presenting an assemblage of characters differing from the bulk of our species. The pale or white worms, some of considerable size, of sluggish habits, and secreting an abundance of slimy fluid belong here; they are provided with eight separated chætæ in each segment, and diffuse nephridia.* But in 1899 Michaelsen(5), the foremost German authority on the group, as a result of the examination of material collected by Schauinsland, suggested further subdivisions of the typical Acanthodrilid type, thus: Maoridrilus for those species presenting the very peculiar alternation of the nephridiopores, which is practically limited to our New Zealand species; while the rest of the common species he referred to Notiodrilus, in which the pores form a single series on each side.
I confess that there is a certain amount of convenience in the subdivision of the genus, but there is no constant character that accompanies this condition of the nephridiopores; nor, indeed, is there any very strict regularity in the alternation in an individual, and when a series is studied it becomes evident that a good deal of variation occurs.
The term “Maoridrilus” may, perhaps, be conveniently used as a subgenus, for it is, anyhow, a remarkable fact that this “alternation” of the pores seems limited to New Zealand species, and occurs also in the genera Plagiochæta and Neodrilus, both confined to these Islands—though it also
[Footnote] * At another time I will present a complete diagnosis of our native species, but at the present I will leave this matter.
arranged in four couples, one couple on each side being latero-ventral, the other latero-dorsal. These couples are nearly equidistant, and form four lines along the entire length of the body. The body of the worm is quadrangular in section, except in the anterior twenty or so segments, and these couples of chætæ are situated at the angles. Each segment, too, is provided with a pair of small but distinct pores at its anterior margin. These are the nephridiopores, the apertures of the excretionary organs. The first pore lies at the anterior boundary of the 3rd segment. A very remarkable arrangement is presented by these pores in many of our New Zealand worms, in that they are situated alternately in front of the upper and in front of the lower couple of chætæ. This alternation is not absolutely regular, and, in fact, up to the 10th or 11th segment they are in line with the upper couple of chætæ.
Further, in the median dorsal line, on each of the inter-segmental furrows, behind the clitellum, is a small dorsal pore, which is, however, not easily seen in preserved specimens.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
The clitellum, or saddle-shaped girdle, covers segments 14–19, and may even encroach occasionally upon the 13th or 20th segments. The glandular thickening of the skin covers the back and passes down the sides as far as the level of the ventral chætæ, leaving the ventral surface free. Within this area, in the hinder part of this region, are four noticeable circular papillæ, usually pale in colour; they lie on the 17th and 19th segments in pairs, in line with the ventral chætæ. Each papilla is provided with a pore—hence they are termed “porophores”—which allows the protrusion of a couple of long, fine bristles, known technically as “copulatory or penial chætæ”—the modified ventral chætæ of these segments. These are about three times the length of ordinary chætæ, and of a different shape (see figs. 9 and 10). The two porophores of each side are connected by a distinct longitudinal furrow, with well-marked lips, passing from the pore on the 17th, across the 18th segment, to the pore on the 19th segment. This “spermatic groove” is straight, and passes between the ventral couple of chætæ of the 18th segment. At this point is situated the “male pore,” the external aperture of the sperm-duct; a minute pore, only visible with difficulty. On the 14th segment are the paired “female pores,” the apertures of the two oviducts, lying just in front of the ventral chætæ. Further forwards, and placed on the intersegmental groove separating segments ⅞ and 8/9, on each side, are the two pairs of spermathecal pores, also in the line of the ventral chætæ.
As in other earthworms, the cavity of the body is subdivided by a series of transversely disposed muscular septa, inserted into the body-wall at the level of the intersegmental furrows, and attached to the wall of the gut at their inner edges. Of these septa, those forming the posterior boundary of the segments 8 to 12 are much thicker than the others. The dorsal blood-trunk is duplicated, but the two tubes unite as they pass through the septa. In addition to this main blood-trunk there is, below it and closely connected with the wall of the gut, a “supra-enteric” vessel in a few of the anterior segments—about 9 to 14—and it is this supra-enteric vessel that gives off the four pairs of intestinal hearts, or, better, “enteric hearts,” which have no connection with the “dorsal” vessel. These “hearts” occur in segments 10–13; each passes round the gut to enter the ventral vessel below the gut. In segments 8 and 9 are two pairs of “lateral hearts,” arising from the dorsal vessel and passing to the ventral; these are, however, smaller and less conspicuous than the other hearts. In the 9th segment the dorsal trunk gives origin to a pair of “lateral” vessels, which run forward on each side of the gut, to break up into a plexus on the pharynx.
The alimentary canal consists of the usual parts. The following dispositons, however, are to be noted: The gizzard occupies the 6th segment; the œsophagus is a cylindrical tube, extending back to the 17th segment, where it passes into the Intestine. In the course of the œsophagus there are marked dilatations in the 14th, 15th, and 16th segments. The walls are highly vascular, and thrown into folds (lamellæ) internally; the “œsophageal glands,” however, contain no lime, as do the calciferous glands of many earthworms. The size of these “glands” is somewhat variable. The intestine is much wider than the œsophagus, is thin walled, and possesses a very slight ridge-like typhlosole.
The nephridia are fairly typical, and call for no special remark here; be it noted, however, that there are evident differences between the dorsal and ventral series of nephridia.
The reproductive system is, however, of importance, as it is characteristic of the family Acanthodrilidæ. We have, of course, to distinguish the male organs and the female organs.
(a.) The Male Organs: There are two pairs of testes, lying in segments 10 and 11 respectively, and attached to the anterior wall of each of these segments. They are quite free, not enclosed in sacs, as is Lumbricus. In the same segments lie the two pairs of funnels of the sperm-ducts, projecting from the posterior wall, or septum, of each of these segments. Two
pairs of lobulated sperm-sacs (seminal vesicles) almost fill the segments 11 and 12. Two pairs of conspicuous, yellowish, coiled tubular glands lie in segments 17 and 19. These are the “spermiducal glands” (or “prostates”). Each gland is connected to the body-wall by a shining muscular duct, which opens by the porophore seen externally; the opposite end of the gland is free. Each gland is accompanied by a short muscular sac, containing the copulatory chætæ aforesaid. When these are examined under the microscope the sac is found to contain two or three chætæ, each of which is long, delicate, hair-like, and gently curved, the tip being somewhat spoon-shaped.
[The functions of these parts is not known with certainty, but in all probability the copulatory chætæ are inserted into the spermathecæ, serving to hold the worms together during the process of copulation, and the secretion of the spermiducal gland aids in this cohesion.]
(b.) The Female Organs: There is the usual pair of ovaries in segment 13, attached to the anterior wall, and behind each is the funnel of the oviduct, a wide, flattish structure, resting on the anterior face of the septum between the 13th and 14th segments; it leads into the short, narrow oviduct that passes through the body-wall in the latter segment to reach the exterior.
There are two pairs of spermatheæ (or copulatory sacs), lying in segments 8 and 9 respectively; each sac opens to the exterior at the anterior limit of the segment, through the pores already noted. The form of the sper-mathecæ is of considerable value in identifying the species of our endemic worms. In A. uliginosus it consists of an ovoid sac, the true “copulatory sac,” reaching across the segment, and free posteriorly; it possesses a muscular duct nearly as long as itself, into which opens a peculiar “diverticulum,” or accessory sac, which usually lies in the preceding segment. This diverticulum* of the duct, which alone contains spermatozoa—received from another worm during copulation—is somewhat variable in size, but its wall presents a considerable number of small rounded pustules on its surface, so that it resembles in its entirety a blackberry. Sometimes this diverticulum is flattened out (when empty); at other times (when distended) it is more or less globular, but always presents the blackberry-like form. The diverticulum is “sessile,” opening directly into the duct of the spermatheca. [In a closely allied species, A. rosæ, it is provided with a distinct stalk.]
[Footnote] * The form of the diverticulum is one of the most readily recognised specific characters in Acanthodrilus.
(1.) Benham: “A Re-examination of Hutton's Types of New Zealand Earthworms.” Trans. N.Z. Inst., vol. xxxi., 1898, p. 156.
(2.) Hutton: “On the New Zealand Earthworms in the Otago Museum.” Trans. N.Z. Inst., vol. ix., 1876, p. 351.
(3.) Beddard: “On the Specific Characters of certain New Zealand Earthworms.” Proc. Zool. Soc., 1885, p. 813.*
(4.) Beddard: “On some New Species of Earthworms from Various Parts of the World.” Proc. Zool. Soc., 1892, p. 668.
(5.) Michaelsen: “Oligochæten v. den Inseln der Pacific.” Zool. Jahrbuch, Abth. f. System, &c., vol. 12, 1899, p. 234.
Explanation Of Plate V.
Fig. 1. Dorsal view of anterior end of the body; twice natural size.
Fig. 2. Ventral view of the segments 11 to 22, showing the extent of the clitellum, the arrangement of the chætæ (as short lines) and nephri-diopores (as small circles), and of the genital pores; × 2.
Fig. 3. Diagrammatic transverse section, showing arrangement of chætæ, intestine, and the difference between the “dorsal” and “ventral” nephridia.
Fig. 4. Diagrammatic view of the first twenty-one segments, showing the alimentary system and part of the vascular system, as seen when the body is out through along the dorsal mid-line and the wall pinned aside; about natural size.
Fig. 5. Part of the vascular system: the dorsal vessel has been removed in five segments to show the “supra-enteric vessel,” with which the large “enteric hearts” are connected. The “lateral hearts” in segments 8 and 9 arise from the dorsal vessel, as do also the two “lateral vessels” in the 9th segment. The supra-enteric vessel is formed by the union of capillaries issuing from the “œsophageal glands.”
Fig. 6. Diagram of one of the ventral nephridia: t, the coiled tubule; f, funnel opening through the septum; bl, the muscular bladder; o, its external aperture.
Fig. 7. Diagrammatic view of the reproductive organs; about natural size.
Fig. 8. A spermatheca, seen from the side: s, main copulatory sac; d, muscular duct; div, diverticulum.
Fig. 9. Normal chæta.
Fig. 10. Copulatory chæta, magnified to exactly the same size as fig. 9.
[Footnote] * Contains a somewhat detailed account of the anatomy of our worm.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|bl.||Muscular bladder of nephridium.|
|buc.||Buccal region of gut.|
|cop.||Sac with the copulatory chætæ.|
|d.||Muscular duct of spermatheca.|
|div.||Diverticulum of spermatheca.|
|f.||Funnel, of nephridium (fig. 6), of spermduct (fig. 7).|
|i.h.||Enteric heart, arising from supra-enteric vessel.|
|L.||Lateral couple of chætæ.|
|l.h.||Lateral heart, arising from dorsal blood-trunk.|
|l.v.||Longitudinal lateral vessel.|
|m.||Pore of sperm-duct.|
|p.||Opening of spermiducal gland on porophore.|
|s.||Copulatory sac of spermatheca.|
|sp.s.||Sperm-sacs, or seminal vesicles.|
|t.||Coil of nephridial tubules. (fig. 6), testis (fig. 7).|
|V.||Ventral couple of chætæ.|