18/6.] MR. PARKER ON THE SKULL IN SHARKS AND RAYS. G99 



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 fol- 

 lowing 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 Raia 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 em- 

 bryos 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 ' grains 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, aud even the spiracular cleft, the 

 fyst postoral opening. 



" These acquire a considerable size ; and I find in Rata 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 he an early ' crop ' of papillae that are 

 clavate, and long ; thev only contain a single branchial loop. 



" The permanent gill-folds arise in the same manner as the ex- 

 ternal gills, hut they are later in appearance; they are a second crop 

 springing among the roots of the first. 



" The first, 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 



