OCR Text |
Show 1892.] NEW SPECIES OF EARTHWORMS. 145 records are scanty. In Criodrilus I mention 1, briefly, the " hemispherical gland, which may be called a prostate," and which " consists of cells similar to those forming the epidermis of the clitellum and quite continuous with them ; the gland appears to be formed only by a hemispherical thickening of the epidermis over this area." Rosa 2 refers to this organ as " atrium." In the case of Callidrilus, Michaelsen3 states that this "doubtful prostate" consists of small granular cells, with indistinct boundaries, the nuclei sometimes being scarcely recognizable ; in the same place he describes-though very briefly-structures of the same nature as those in Micr. papillata as occurring in Kynotus madagascariensis; to which I shall refer later on in this paper. The nature of the organ in Geoscolex is unknown. But Micro-chtfta (and probably Kynotus) differs from the rest in that this gland is entirely independent of the sperm-duct; whereas in pros-tatiferous worms (that is, those of the families Cryptodrilidee, Perichcetidce, Acanthodrilidce, Eudrilidce, &c.) this gland is always in connection with the sperm-duct, or in its immediate neighbourhood ; moreover, it is tubular in general character and is apparently a more efficient organ of copulation than in these other cases. W e are in ignorance of the real function of the prostate or of the " genital duct" in these prostatiferous worms ; but there is, probably, a protrusion of the muscular duct during copulation, and an insertion thereof into the spermatheca, as there is undoubtedly in such forms as the Tubificidce: but in the case of Microchceta such a penial function is impossible, for there is no sac into which such a papilla could be inserted; it probably, however, serves as a sucker. The small papilla in the terminal pit of the larger one, the muscular arrangements, and the folded cavity suggest such a sucking-organ ; and, no doubt, the copulating chaetae serve to aid this apparatus in holding on to another worm 4. It is not necessary to think that this sucking-apparatus in Microchceta is the forerunner of the prostates with their protrusible duct, though it is quite possible that this latter organ may have arisen from some such apparatus as is present in Brachydrilus, Geoscolex, &c.,,where the "sucker" is perforated by the sperm-duct. During copulation in Lumbricus, &c, the ventral surface of the clitellum itself, bounded by the tubercula pubertatis, very probably acts as a sucker; here in Microchceta a more specialized apparatus, on 1 " Studies in Earthworms, III.," Q. J. M. Sc. xxvii. p. 568. 2 "Sul Criodrilus lacuum," M e m . d. E. Accad. d. Sci. d. Torino, ser. 2, torn, xxxviii. 3 « xerricolen d. Berliner Zool. Samml.," Arch. f. Naturgesch. 1891. 4 Rosa describes (Ann. d. k. k. Natur. Hofmus. 1891) certain glandular bodies in M. benhami (in somites xi. to xxviii.) which appear to have a somewhat similar structure; but he mentions no external papillae: he compares them with the " pyriform glands " of Urobenus and JJrochceta, and suggests, as I have done, their possible connection with the prostates of other worms ; and his species forms an interesting link between the arrangement in Urobenus and M. papillata, though the structures in M. benhami do not appear to have any copulatory functions. P R O C ZOOL. Soc-1892, No. X. 10 |