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Show 884 MR. W. WOODLAND ON THE [Nov. 27, the base of the tail, i. e. towards the cloaca, this supra-neural vein breaks up first into two smaller veins situated to the side of but still above the nerve-cord, and still more anteriorly into a number of very small veins which soon become lost between the constituent masses of the myotonies. In the adult the vein (which is very obvious) lies immediately ventral to the elastic ligament mentioned above; in the embryo examined this ligament was not at that stage developed (fig. 8, PI. LVIII., represents a section Text-fig. 138. Centrophorus calceus. Diagram of section of posterior caudal vertebra, showing position of the supra-neural vein (S.V.); E.L., elastic ligament. through an anterior caudal vertebra, hence the supra-neural vein is not shown there). The formation of this supra-neural vein by the fusion of numerous lateral veins is a forcible illustration of the production of median vessels by fiexion of the body which I have elsewhere 3* insisted upon. I have not been able to discover a similar supra-neural vein in the Common Dogfish, and apparently there was not one present in a large specimen of Echinorhinus sjyinosus which was examined for me at Plymouth. EXP LAN A TIO N OF THE PLATES. P l a t e L V I I. Centrophorus calceus. Fig. 1 . Cloacal region. L.A.P., left abdominal pore; OD., oviduct; K., rectum; R.A., opening of rectum into cloaca ; R.A.P., enlarged right abdominal pore ; R.G., rectal gland ; R.O.A., right oviducal aperture ; U.P., urinary papilla. 2. Scales from dorsal and ventral surfaces of body. P.P., basal plate; T.S., tritid spine. 32 " On a New Mode of Persistence of the Posterior Cardinal Vein in the Frog (Eana temporaria) : with a Suggestion as to the Phylogenetic Origin of the Post- Caval Vein." Zool. Anzeig. Bd. xxviii. (23) 1905. |
