ENDOSKELETOX. ANIMALS. 21 



A. 66. Anterior portion of the body of Bdellostoma cirrhatum. 



The soft parts have been removed from the left side to show 

 the cartilaginous skeleton. 



A. 67. Piece of the jaw of a Shark. Near the surface of the 

 cartilage is a layer of plates of calcified cartilage. 



Hunter ian. 



A. 68. Two portions of the layer of plates of calcified cartilage, 

 one showing the deep, the other their superficial surface, 

 from a Shagreen Ray (Raja fullonica). The plates are 

 mostly hexagonal, and about 0'8 mm. in diameter. The 

 outer surface of the plates is flat, the deep surface has 

 strong ridges that radiate from the centre, and are in 

 number equal to the sides of the plate and at right angles 

 to them. A thin layer of uncalcified cartilage commonly 

 invests the surface. 



Leydig, Beitr. A nut. u. Entwickl. der Rochen u. Haie, 

 1852, p. 4. 



A. 69. Cartilaginous skeleton of a young Ray (Raja maculata). 



A. 70. Skeleton of a Sterlet (Acipenser rutkenus). It is largely 

 composed of cartilage. The bone contains lacuna) with 

 numerous canaliculi. The cranial bones forming part of 

 the exoskeletou have been removed from the left side. 

 Klaatsch, Morph. Jahrb., Bd. xvi. 1890, p. 233. 



A. 70 a. Skeleton of Bony-Pike (Lepidosteus osseus), chiefly 

 composed of bone. 



A. 71. Skeleton of a Haddock ((jradug cuykjinus), and drawing 

 of the bone structure. The bones of Gadida; consist of 

 matrix in which are spaces occupied by fluid, and various 

 sized droplets of organic matter that stain readily bv 

 reagents. There are no blood-vessels or included cells. 



A. 72. Skeleton of a young Sword-fish (Xiphias gladias), with 

 drawings of the microscopic structure of the bone. It 

 consists of matrix disposed in concentric layers around the 

 numerous blood-vessel-containing channels (Haversian 

 canals.) There are no included cells, but from a few of 



