Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/724

Rh 682 WORM (Eisen) the prostates are very numerous, and arranged in pairs ; in Psammoryctcs (Vejdovsky) and in Hemttubiftx (Eisen) the upper part of the vesicula seminalis, into which open the vas deferens and the prostate, forms a globular chamber distinct from the re mainder of the atrium. Another type of efferent apparatus is found in the Liimbriculidae. In Stylodrilua there is a single pair of atria, which have much the same structure as in Stylaria, but the proximal end of the organ is less glandular and can be everted as a penis. With each atrium, however, are connected two vasa deferentia ; one of these opens by a funnel-like expansion into the segment in front, the other passes back into the segment behind that &quot;which contains the atrium, and after again perforating the septum opens by a funnel-shaped ex pansion into the atrial segment. Among earthworms Moniligaster, as already stated, is furnished with an efferent apparatus exactly comparable to that of the lower &quot; Limicolie.&quot; In other genera the same divisions can be recognized in the efferent apparatus, which may also be single or double. In all earthworms, however, with the exception of Moniligaster, the internal funnels are situated several segments in front of the external pore, instead of being placed in the next segment. This is the case also with Ocncrodrilus (Eisen), a form usually referred to the &quot; Liniicolas.&quot; Urocliieta and Typh&us are the only genera known, besides Moniligaster, in which there is a single vas deferens on each side. In all others there are a pair of vasa deferentia on each side, which open by separate funnels into two consecutive segments (10th and llth) ; the vasa deferentia open on to the exterior by a common pore ; they may become united into a single tube in the segment behind that which contains the posterior funnel (Lumbrieus, Perichteta), or one or two segments farther back (Microchxta), or, finally, as in Eudrilus, they may unite in the terminal apparatus. The structure of the vasa deferentia and the funnels corresponds to that of the lower Oliaochseta, except that the funnels are usually much plicated. In Lumbrieus, Uroch&ta, &c., the vasa deferentia open directly on to the exterior ; in other types, however, an atrium can be recognized. The most primitive form of these organs (in some respects) is seen in the genus Eudrilus (Beddard, 3); the two vasa deferentia open into the interior of a glandular organ, which is probably the homologue of the atrium ; this organ is divided into two parts by a longitudinal septum, but is covered by continuous layers of muscles ; it communicates with two muscular tubes, also covered by a continuous layer of muscle, which unite into a single muscular penis, which is probably eversible. The penis, like the atrium, is lined by a single layer of non-ciliate cells; the cells of the glandular portion are non-ciliate, and are arranged in two layers ; the penis projects into the interior of a cavity open to the exterior ; this corresponds to the penis sheath of the NaidomorjiTia. With the penis sheath (&quot;bursa copulatrix,&quot; Perrier) is also connected a small rigid diverticulum with muscular walls. It is not certain whether the partial longitudinal division of the atrium and vesicula represents the partial fusion of the primitively distinct atria or the commencing separation into two parts of a single atrium ; the latter alternative, on the whole, is the more probable. In Pcrichieta, Acanlhodrilus, &c., certain glandular bodies are connected with the termination of the vas deferens, which have been termed &quot;prostates.&quot; These glands are of two kinds: (1) in Acan thodrilus, Pontodrilus, &c., they consist of a single somewhat con voluted tube of uniform diameter ; (2) in Perichseta, &c., they have a racemose lobulated appearance. It is probable that these structures are homologous. The prostates of Perichieta (fig. 5, F) are made up of numerous ductules, which are connected with groups of cells that have the character of unicellular glands ; each cell is connected by a long stalk with the termination of the ductule ; in Acanthodrilus, &c., the prostate is lined by a double layer of cells which surround a central lumen ; the innermost layer of cells are narrow and columnar, the outer layer are large pear shaped glandular cells. The difference between the two organs is this : in Pcricfiieta the glandular cells have become segregated into groups, while the lumen of the gland is branched. In at least one species of Perichieta both these differences from Acanthodrilus are less marked. The so-called prostates of Acanthodrilus and Pontodrilus agree in their minute structure with the vesicula seminalis of Eudrilus, and they open on to the exterior, like the corresponding structures in Perichieta, by a thick-walled muscular tube ; the vas deferens, however, is connected in Pontodrilus with the muscular part of the atrium, and not with the vesicula ; the condition of the efferent apparatus is therefore a more modified one. In Typhieus this modification is carried still further: the vas deferens enters the body- wall independently of the vesicula and atrium, and only joins the k.? ., cl(n y the epidermis just before its opening on to the exterior, t ejdovsky be right in interpreting the so-called receptaculum nmis of Ocnendrilus (Eisen) as the atrium, the relations of the several parts of the efferent system in this worm are much the same as in Typhous. In Acanthodrilus (fig. 5, H) the two pairs of atria open on to the 17th and 19th segments respectively: the vasa deferentia open on to the 18th independently of them. .) Genital Setae. It is commonly the case among the Oligochxta that the setae upon the clitellnm, in the neighbourhood of the spermathecre and the male sexual apertures, undergo a certain amount of modification. Thus in Lumbrieus the setae in these regions of the body are longer and more slender than the sette else where (Hering) ; in Urochseta and Thamnodrilus the setae upon the clitellum are ridged. Analogous modifications are found in Nais and other &quot; Limicolse.&quot; The function of these setae is prob ably, as Lankester has suggested, to assist in attaching the worms together during copulation. Before the individual is mature these setae are absent, and the ordinary setre occupy their place ; when the clitellum is developed the ordinary setse drop out, and are replaced by the genital setae (Vejdovsky). In Acanthodrilus, Typh&us, and some species of Perichseta the apertures of the atria are furnished with a thin-walled muscular diverticulum in which are found a bundle of extraordinarily long sete ; these can be protruded through the sexual orifice and may possibly serve to assist in the transference of the sperm to the spermathecffi of another individual. These setae may be termed &quot;penial&quot; setae (Lankester) (fig. 2, a, b). (2) Female Reproductive Apparatus (a) Ovaries. The ovaries of Lumbrieus were first discovered by D Udekem ; they consist of a pair of minute pear-shaped bodies attached to the anterior septum of the 13th segment (fig. 4, o); their position exactly corresponds to that of the testes, and like those organs they are covered by a delicate layer of flattened peritoneal cells. In Pcrich&ta and Acanthodrilus, where the testes are prolonged into numerous digi tate processes, the ovaries have an identical form ; finally, the contents of the young ovaries and testes consist of entirely similar germinal cells (Bergh) ; these facts all tend to prove the serial homology of the ovaries and testes. With the exception of Eucli- pidrilus and Phreoryclcs, the Oligochazta possess but a single pair of ovaries, which appear to be invariably 1 placed behind the testes. (b) Receptaculum Ovorum. Corresponding to the seminal reser voirs are a pair of outgrowths from the posterior side of the septum which separates segments 13-14 ; the ripe or nearly ripe ova are stored in these receptacles. Their presence in Lumbrieus was first discovered by Hering. They have the same structure as the seminal reservoirs ; their cavity is similarly divided by anastomosing trabeculse; and they have been proved by Bergh (19) to originate in the same way. In Moniligaster (Horst) these bodies are of large size, and therefore resemble more closely the seminal reservoirs. They are generally present in earthworms. Among the Naido- morpha organs are met with which appear to resemble the recep- tacula. In Stylaria lacustris a pair of delicate sacs are developed in the same segment as that which contains the ovaries ; in these the ova undergo their development ; the extremity of the sac encircles the ovary, so that the ova can readily find their way into it. This organ is, however, compared by Vejdovsky (15) to the delicate peritoneal covering of the ovary in Lumbrieus, and more particularly to a tube-like projection of this peritoneal covering at the free extremity of the ovary where the ripe ova are found. (c) Oviduct. The oviducts in Lumbrieus are two minute trumpet- shaped bodies composed of a single layer of ciliated cells ; the funnel-shaped expansion opens into the 13th segment; the tube perforates the mesentery, and opens on to the exterior in the 14th segment. The mouth of the oviduct is in close relation with the aperture of the receptaculum ovorum into the same segment. In most earthworms a pair of oviducts of similar structure have been recognized ; in Perichaeta the two oviducts open by a common pore situated in the median ventral line of the 14th segment. The aper tures of the oviducts are, with the exception of Moniligaster (Horst) and Allurus (Beddard, 5), invariably placed in front of the male gene rative r pores. Among the &quot;limicolous&quot; forms oviducts have been described in Rhynchelmis, Phreoryctcs, and Phreatothrix ; in these genera, however, the oviducts consist of little more than the funnel which is sessile on the ventral body-wall of the llth segment, and opens on to the exterior in the groove between this and the following segment ; in Phreoryctcs, Beddard (6), there are two pairs of oviducts entirely contained in one segment. It is important to note that in Rhynchelmis and Phreatothrix the female pore is behind the male pore, while in earthworms (except Moniligaster, Allurus) it is in front. Among the lower Oligocheeta oviducts are absent ; their place is taken in the Enchytrmdss and others by a pair of slit-like orifices placed on the clitellar segment behind the apertures of the vasa deferentia. That these pores represent the external orifices of the oviducts in the higher forms is shown by the following considera tions : (1) their position behind the male pores ; (2) the probability urged by Vejdovsky that the clitellar segment really represents three fused segments, in which case the oviducal pores arc really one segment behind the male efferent pores ; (3) the remarkable analogy with the Cyclostomata among fishes, where the abdominal pores act as oviduct (Weber, Zcitsch.f. iviss. Zool., 1887). The ovaries and oviducts of Eudrilus (Beddard, Horst), differ in many particulars from those of other Oligochseta. The ovaries (fig. 6) are two solid bodies situated on the anterior septum of segment 1 Phitellus is, according to Perrier, an exception ; the ovaries arc in front of the testes.