SHARKS AND RAYS. 21 



fishes, in Wall-case 12, together with the Archer-fish and the 

 Perch, and in "Wall-case 13 there follow the Sea-perches, 

 Basses and Meagres. The Snappers, Sea-Breams, Bed Mullets 

 and Chcetodont fishes are shown in Wall-case 14, and the 

 Surgeon-fishes, Parrot-fishes, Wrasses and Mackerel-like fishes 

 in Wall-case 15. 



The small Wall-case 16 is devoted to the Horse-Mackerels, and 

 Wall-case 17 to the Frost-fishes and Dolphin-fishes. Wall- 

 case 18 includes the Dorys,the Flat-fishes, such as the Sole, Plaice 

 and Turbot, and the Sucking-fishes and Gobies. In the upper 

 part of Wall-case 19 are exhibited life-sized coloured drawings of 

 the Bibbon-fishes, and in other parts of the case are specimens of 

 Gurnards, Lump-suckers and Blennies. The systematic series 

 ends with Wall-case 20, which contains the Angler-fishes (on the 

 floor), the File-fishes, Globe-fishes and Sun-fishes. 



ELASMOBRANCHII (Sharks and Bays). 



The Elasmobranchii, including the Sharks, Dog-fishes, Saw- Wall- 

 fishes, Skates and Bays, are marine fishes with a skeleton composed case *• 

 of cartilage, the surface of which is usually calcified, but does not 

 exhibit the characters of true bone. The skin possesses tooth-like 

 structures called placoid spines, which when closely set constitute 

 shagreen. The vertebral column is in most instances continued 

 into the upper part of the tail fin, and the lower lobe is small as 

 compared with the upper; such a tail is known as " heterocercal." 

 The fins are supported by closely-set rods and plates of cartilage 

 in the basal parts, and by horny fin-rays in the marginal parts 

 (see specimen 3). There is no gill-cover, and, with a few ex- 

 ceptions, five gill-slits open on each side of the body. The heart 

 has a chamber known as the conns arteriosus, which is provided 

 with watch-pocket valves that prevent the return of blood to the 

 ventricle (see dissection 2) . The intestine has a spiral valve (see 

 dissection 1) and there is no swim-bladder. The ova or egg-cells 

 are large, and undergo their development either within the body of 



