| OCR Text |
Show 1885.] NEW-ZEALAND EARTHWORMS. 827 are equivalent to the "soies de remplacement " of the locomotor setse; these, however, are contained within the body-cavity and do not protrude on to the exterior. It is important to notice that the genital setse, although different in appearance from the ordinary locomotor setse, do not differ in their disposition ; and, moreover, the aperture of the conjoined vas deferens and prostate duct has a relation to the setaa precisely similar to that which has already been referred to in the case of the nephridial aperture and the locomotor setas (see p. 822). The apertures of the vasa deferentia, like those of the nephridia, correspond in position to the outermost setse of the pair. § Female Generative Organs. In Acanthodrilus nova zelandia and A. dissimilis the ovaries are to be found in the 13th segment, i. e. next to that which contains the posterior pair of testes ; they are attached to the anterior mesentery of this segment close to the middle line. The ovaries are of a very peculiar form ; instead of being round, or, rather, pear-shaped as in Lumbricus, they present the appearance of a flattened circular disk, much folded and plicated ; their resemblance indeed to a vas-deferens funnel is so striking, that T mistook them at first for such a structure, until a microscopical examination revealed their true nature. I find a figure by M . Perrier of the ovary of Perichata houlletT, which shows a great resemblance to the ovaries of this Acanthodrilus. It is interesting to note the different positions which the ovaries may occupy in Earthworms : in Lumbricus they are situated on the anterior wall of the segment in which they are found, and, as in Acanthodrilus, this is the 13th segment of the body ; in Perichata and Microchata the ovaries are found in the same segment of the body, but upon the posterior mesentery ; in Acanthodrilus multiporus I have to record the position of the ovaries in the same segment, but attached to the anterior margin of the oviduct-funnel and apparently to the ventral body-wall, between the two mesenteries which enclose the segment. In Acanthodrilus dissimilis, also in A. nova zelandia, the oviducts open separately in front of the ventral pair of setse of each side ; a series of transverse sections through this region show that the apertures bear a particular relation to the outermost of these two setse. There is nothing remarkable in the structure of the oviducts. The oviducts of A. multiporus open by the innermost of the two ventral setse, so that the position is slightly different. In all three species there are a series of peculiar glands, two pairs situated in the 11th and 12th segments. The position of these structures in A. dissimilis and A. rova zelandia is shown in the drawing (woodcut, fig. 3) which illustrates the generative region of A. dissimilis. The general appearance of these glands is not unlike that of the ovaries ; they are somewhat rosette-shaped, being formed of a much plicated disk, attached by a narrow pedicle to the anterior mesentery, and depending freely into the interior of the segment; the general 1 Nouv. Arch. &c. loc. cit. pi. iii. fig. 60. |
