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Show 1892.] SPECIES O F E A R T H W O R M S . 693 funnel of the nephridia, which lies in the segment in front of that which contains the rest of the nephridia. The structure of the nephridia is not that of the aquatic Oligochaeta ; they recall those of the Geoscolecidae. It is of course the reproductive organs which are so different from those of the higher Oligochaeta. The testes, as in the other species of the genus, are placed within the sperm-sacs attached to the front wall of segment x. ; they are also in contact with the ciliated rosettes, which open likewise into the interior of the sperm-sacs. In Moniligaster barwelli I figured and described the ciliated rosettes as lying in the same segment as that upon which the atria open on to the exterior ; this is also the case with M. beddardi and with the species described in the present paper; in those two Moniligasters the sperm-duct is very short and lies entirely within the xth segment. In M. bahamensis the sperm-ducts are remarkably long and much convoluted, recalling the sperm-ducts of such genera as Pachydrilus ; they do not lie entirely within the xth segment but extend forwards into the segment in front. It is quite possible that the difference is merely one of maturity in the various individuals. The arrangement of the sperm-ducts is, curiously, the reverse of the arrangement characteristic of the posterior sperm-duct of the Lumbriculidee ; in these worms the sperm-ducts in question traverse the septum lying behind the male pore, and then bend back to traverse the same septum again. This is exactly what occurs in Moniligaster bahamensis, only that it is the segment in front of that which bears the male pores which is twice perforated by the sperm-ducts. I do not, of course, intend a serious comparison between the two forms in this matter ; but at any rate the disposition of the sperm-ducts in Moniligaster is exceedingly different from anything that occurs in the remaining genera of Earthworms. The sperm-sacs in the present species are restricted to the xth segment; this was the case at any rate with one of the two species which I studied by means of longitudinal sections ; the segment in which they lie is the xth ; as in the other species of the genus, their cavity is undivided by traheculae, but filled with developing sperm. The orifices between segments x./xi. lead into a pair of muscular sacs ; each sac has a narrow lumen bordered by a single layer of low columnar cells covered with a moderately thick chitinous layer ; outside the epithelium is a mass of muscles which are somewhat loosely arranged, and in the interstices of which lie groups of glandular cells. The sac is oval in form and at the distal end the lining epithelium is reflected back over a conical process which contains the duct of the atrium proper ; the terminal sac with this evidently protrusible structure has clearly the closest possible resemblance the penis and penis-sheath of the Tubificidce. Vejdovsky has figured1 a protrusible penis in the Lumbriculid Stylodrilus-a family which is in some respects nearer to Moniligaster than are the Tubificidae. Among Earthworms the nearest approach to the penis 1 System, u. Morph. Oligochaeten, pi, xi. figs. 11-16. |
