OCR Text |
Show 226 MR. A. ALCOCK ON A VIVIPAROUS [Apr. 7, This completes the subfamilies and recognizable genera of Slugs. I have in this paper preferred to give the facts almost without any discussion of the problems illustrated by them, partly because such a discussion would be more suitable in connexion with a paper of less limited scope, and partly because it would render the present contribution unduly long. 2. O n a Viviparous Bathybial Fish from the Bay of Bengal. B y A. A L C O C K . M.B.. Surgeon I.M.S. (Communicated by Prof. J. W O O D - M A S O N , F.Z.S.) [Eeceived March 16, 1891.] In the 'Annals and Magazine of Natural History' for November 1889 (vol. iv. ser. 6, pp. 389-390), I described under the name of Saccogaster maculata a new type of Brotuline Ophidiids allied to Catcelax. The two specimens upon which the genus was established were described as females 3| and 4 inches long, with gravid ovaries; they were taken in 193 fathoms off the mouths of the Gangetic Delta. Among the characters which distinguish Saccogaster the two most marked are its sac-like abdomen and its loose imperfectly-scaled skin. On the 24th December last, in a very successful haul of the trawl in 240 fathoms off the mouths of the Kistna Delta, another specimen of Saccogaster maculata was obtained. It proved to be an adult male, 3^ inches long, with ripe milt. Though otherwise resembling the female in external characters, it differs in having a deep post-anal depression or excavation, which is filled by a large bilobed papilla with the genital pore opening into the groove between the lobes. The papilla is thick, fleshy, and smooth ; each lobe is about 2 m m . long and L25 m m . broad, and is pigmented at the apex. In consequence of the discovery of this genital papilla a microscopic examination of a portion of one of the ovaries of the original type specimen was made, and it was found that in the ova as they lie in situ the development of the embryo is already far advanced. Unfortunately the material is not in the best state of preservation, but the ova are still in a sufficiently good condition to show the general relations of the embryo. The embryos are vermiform ; they are about 1*5 m m . in length, and are closely applied to the yolk-sac, which they embrace through rather more than three-quarters of its circumference ; the cerebral lobes, optic vesicles, and long free tail-fold are plainly apparent, but beyond these and the continuous bright line of the notochord nothing can now be made out; the yolk-sac is a little more than |