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Show 174 MR. F. E. BEDDARD ON A LARGE EARTHWORM. [Mar. 16, my species, however, these structures are in the same segment as which contains the anterior spermatheca and are not in a segment intercalated between those which contain the anterior and posterior pairs of spermathecae respectively. One of the setae is displayed in the drawing (fig. 3), and the lower extremity, more highly magnified, in another drawing (fig. 4) ; the general aspect of these setae is very similar to that of the penial setae. The seta is curved slightly towards the extremity ; its thickness diminishes gradually until near to tbe distal extremity, where it becomes again thicker and terminates in a swollen brush-like extremity, the exact shape of which can be gathered from an inspection of the figure. The distal extremity of the seta is ornamented with delicate transverse ridges projecting like the edges of scales and denticulated. In Lumbricus Hering1 has described, and Vejdovsky2 confirmed for other species, the modification of certain of the setae in the neighbourhood of the genital orifices ; those of the ventral pair in "the 10th, 15th, or one of the neighbouring segments, and furthermore in the region of the 26th segment and on the clitellum from segment 31 to segment 38 ": these setae are more slender than, and double the length of, the ordinary setae of the body. In the work referred to Vejdovsky goes on to point out that the penial setae in Acanthodrilus and other genera probably correspond to these and differ from the genital setae of Choetogaster &c, which are developed during the breeding-season in the neighbourhood of the ordinary locomotor setae, and in addition to them ; the penial setas of Acanthodrilus replace the ordinary locomotor setae. Since in Lumbricus the modified setae developed in the generative segments are not confined to a single segment or even to the segments bordering upon the male generative pores, it is perhaps not surprising to find that in the present species of Acanthodrilus there are additional sacs of penial setae besides those normally found in the 17th and 19th segments of the body. The modified setae of Lumbricus are also furnished with a gland which projects into the body-cavity; these are apparently the capsulogenous glands of D'Udekem and Lankester, which are the equivalents of the setigerous glands, being simply enlarged in order to assist in the generative function. In Acanthodrilus multi-porus I have figured a pair of glands 3 corresponding to the setae which are probably the homologues of these glands, and I imagine that in the species of which the present note treats the two large glands related to the modified setae of segment 8 are in all probability to be referred to the same category and are not special structures. After the foregoing notes on the structure of this Earthworm I may briefly refer to those points which seem to indicate that it is a distinct species differing from both the other two Acanthodrili which inhabit N e w Caledonia. With regard to external characters it appears to agree with A. ungulatus in the segments occupied 1 Zeitschr. f. wiss. Zool. Bd. viii. p. 418. 2 System und Morphologie der Oligochaeten (Prag, 1884), pp. 156-7. 3 Ann. Sc. Nat. 7C serie, t. xix. pi. i. fig. 6 b. |
