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Show 1900.] ANATOMY OE POLYPTERUS. 431 published of the anatomy of Polypterus are either deficient or inaccurate. In the present paper, I have described in detail the urinogenital system of the male and female Polyptents, together with the later stages of the development of these organs. I have also added observations upon the vascular system, the external gills, the abdominal pores, the anal fin, and the skull. In obtaining m y material, I was aided by a grant of .£50 from the Balfour Fund of the University of Cambridge. The work has been done in M r . A d a m Sedgwick's laboratory. To M r . Sedgwick, Mr. Graham Kerr, and Prof. Howes m y thanks are due for much help and advice. The 3Icde Organs.-In the adult male Polypterus a ridge of testicular tubules extends on either side the entire length of the body, but is only functional towards the anterior end of the ridge, where it swells out to form a conspicuous lobulated testis. A longitudinal duct lies at the base of the whole ridge ventral to and parallel with the ureter. Into this duct the tubules of the testis and of the testis-ridge open by very numerous short ducts. The duct on either side leaves the testis-ridge as the " vas deferens," and running backwards in the same sheath of connective tissue as the ureter, opens upon a papilla into the urinogenital sinus just before the latter opens to the exterior. The spermatozoa are very small, about the length of the long axis of a red blood-corpuscle, slightly swollen anteriorly, tapering posteriorly. The duct of the testis-ridge is developed before the tubules of either the testis or testis-ridge, but in a specimen 9 cm. in length ends blindly in the wall of the ureter. The Female Organs.-The funnel-like openings of the oviduct into the body-cavity were mentioned and figured by Joh. Muller and again by Hyrtl. According to Hyrtl, the two oviducts unite to form a urinogenital sinus, into which the two ureters open by a common mid-dorsal aperture. I find, however, that the ureters are dilated posteriorly, lying closely approximated to one another, but not communicating except immediately before opening to the exterior. Shortly before they open to the exterior, the oviducts open into their lateral walls precisely as do the vasa deferentia in the male. Further, in the young female, 9 cm. in length, the course of these ducts has exactly the same relation to the ureter as in the male, only that the oviducts are considerably more dilated in the female. The ducts at this stage, like those of the male, end blindly in the lateral wall of the ureter. The peritoneal opening of the oviduct is already open at this early stage. The ovary of Polypterus develops as a genital ridge lying on either side along the ventral surface of the kidney, from which it is separated posteriorly by the oviduct. The ovary becomes early divided into numerous compartments, on the external walls of which the ova are developed. 29* |