[ 189 ] 



V. On the Structure and Bevelopment of the Skull in Sharks and Skates. 

 By W. K. Parker, F.R.S. 



Eeceived November 6th, 1876. Bead November 7tli, 1876. 



[Plates XXXIV.-XLII.] 



Inteoductokt Eemarks. 



Through the kindness of my Mends Henry Lee, Esq., F.L.S., and F. M. Balfour, 

 Esq., B A., I am able to give illustrations and descriptions of this type of skull in a 

 degree of detail beyond what I had ever hoped to accomplish. 



Embryos and well-grown individuals of Dog-fish and Skates have been liberally 

 supplied me by Mr. Henry Lee ; these have been from the Brighton Aquarium ; the 

 embryos of Pristiurus and of Scyllium, kindly given to me by Mr. Balfour, were 

 obtained from the Aquarium at Naples. 



As the youngest of these long, delicate, vermiform larvae were not more than two 

 thirds of an inch in length, the head forming a small knob, as it were, to a long and 

 highly flexible staff', it may be imagined how minute these objects were for operating 

 upon by dissecting-instruments. 



By zeal and patience the task has been mastered; these small heads have been made 

 to disclose most important morphological secrets. If any biologist lives who is ready 

 to deride this minute work, I would ask him to close his eyes to what is here shown 

 him, and then give a full explanation of what is presented to him in the skull of an 

 adult Skate or Shark. 



As the Osseous Fishes have undergone a large amount of metamorphosis or speciali- 

 zation, as compared with these Selachians, more than is seen in the Ganoids, it 

 seems natural that the Selachians should stand in a low place, zoologically. This, in 

 many respects, would be, for them, a false position ; for, embryonic as they are, in 

 certain respects, in their adult state, yet they are, on the whole, a very high kind of Fish. 

 They are ^harply separated from all fishes, except the Marsipobranchii, by the non- 

 related condition of their exo- and endoskeleton. Even in the Ganoids the exoskeletal 

 scutes are brought under the influence of the endoskeleton in the head ; and this inner 

 framework draws, as it were, any and every convenient dermosteal patch into harmony 

 with itself, enshielding itself with the enamelled pieces, which take on an outline that 

 makes them apt for any such defensive service. 



VOL. X.— PART IV. No. I.— March 1st, 1878. 2 e 



