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Show 324 ON THE GENITALIA OF BRITISH EARTHWORMS. [Mar. 28, is evidently the homologue of tbe additional gonads on the 12th somite described above in the adult Allolobophora and Lumbricus; and I believe that when we know more of the development of other Earthworms, this additional pair of gonads will be found to be present in most of them at one stage of their existence. In three very young worms (L. terrestris1?) I found this pair of gonads present, and I think that Bergh possibly overlooked it in his account of tbe development of the genital glands, as, from the number of adult specimens of Lumbricus and Allolobophora iu which I have found this pair of gonads, I think that it is in all probability always developed in the embryo, as in Acanthodrilus, but generally disappearing in the adult. The receptacula ovorum were in this specimen, and as I have frequently observed in other Allolobophora, totally disconnected from the oviduct ; in fact, if the development of the former be studied (as can easily be done in young worms) they may be found to arise as outgrowths of that portion of the coelomic epithelium covering the anterior face of mesentery 13/14, dorsal to and quite independent of the oviducts, whose ciliated epithelium may subsequently extend up to their openings. To represent these receptacula ovorum as outgrowths of the oviducts is, I think, erroneous and misleading, as they are the homologues of the seminal vesicles ; and, like them, they arise as hollow outgrowths of the mesenteric septa, and their connection with the oviducts (when effected) is a secondary one. EXPLANATION OF PLATE XXIV. Fig. 1. Longitudinal vertical section of an abnormal Allolobophora longa, x20. t2, posterior testis; /, seminal funnels ; k, hermaphrodite gland ; ov1, ov2, ovaries ; ovd, oviduct; m, mesenteric septa; s.o, segmental organ; n, nephrostome; o.m, oblique mesentery; c.v.d, coiled portion of vas deferens. 2. Eight additional genital gland (testis) from segment 12. a. Entire gland clarified, X 20. b. Part of free end, X 320 : m, mulberry-shaped masses of developing spermatozoa. c. Portion showing bundles of ripe spermatozoa (sp). 3. Base and apex of normal testis, X 320: s, typical sperm mother-cell enlarged. 4. Hermaphrodite gland from segment 12: ov, ova; sp, young sperm mother-cells, x320. 5. (a) Base of normal ovary, X640; (b) single ripe ovum with archo-plasm, X320. 6. Additional ovary from segment 14, X 320. 7. Mass of ova (? ovary) from below the oblique mesentery (o.m) of segment 13 : c.p, epitheloid capsule, X 110. |
