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Show 187t).] MR. PARKER ON THE SKULL IN SHARKS AND RAYS. 699 the body to go eel-fashion. At any rate, they decidedly object to be kept any length of time out of the water : they put up with it for a few minutes, but then begin to plunge about so that I am always glad to get them back again into the water, fearing that they may injure themselves. " I am indebted to Mr. B. Travis, of Maryborough, and to my brothers, Messrs. John and Percy Ramsay, for these specimens." Mr. W. K. Parker, F.R.S., read a memoir "On the Structure and Development of the Skull in Sharks and Rays," of which the following is an abstract:- "The materials for this paper have been kindly given me by my friends Mr. Henry Lee, and Mr. F. M . Balfour : the former obtained them from the aquarium at Brighton, and the latter from that at Naples. " The illustrations of the Shark's skull are from embryos and adult specimens of the Lesser Spotted Dogfish (Scyllium canicula) ; the Skates were of three species, namely Baia maculata, R. clavata, and a species of Pristiurus ; the smallest embryo of the Ray was of this last kind ; this and the smallest Scyllium canicula were two thirds of an inch in length. "The structure of the cranium proper and the facial arches has been worked out, from their first differentiation in the smallest embryos up to their adult condition. The Selachians present a curious and instructive problem in the skull, inasmuch as they only have the cartilage of which it is composed hardened superficially by tesserae of calcified cell-patches, and the dermal bones ('placoid' gsains and spines) are not modified in relation to the endoskeletal parts. " Also we see that in these types the cranium and facial arches are more developed, as to mass in the former, and as to subdivision in the latter: the facial arches, all of which, behind the mouth, carry gills, are here almost typical; they make a useful standard by which to measure those of other Vertebrates. " But the Selachians are of great interest also because of the free development in them of external gills. I find four on each side both in Scyllium and in Pristiurus, and even the spiracular cleft, the first postoral opening. " These acquire a considerable size ; and I find in Baia maculata four more papillae are added, which do not grow outwards, but add to the number of folds in the ' pseudobranchise' of the mandibular suspensorium. "The numerous external branchiae of the hyoid and proper branchial arches are seen to be an early ' crop * of papillae that are clavate, and long; they only contain a single branchial loop. " The permanent gill-folds arise in the same manner as the external gills, hut they are later in appearance; they are a second crop springing among the roots of the first. "Thefirst, or external gills, are buddings from the skin on the edge of the facial bar, close behind the raised opercular fold ; the second upgrowth of filaments lies a little within the first; and on those |
