PISCES 



227 



fish together. Angel sharks are transition types between sharks 

 and the skates and rays. They have large pelvic and pectoral fins, 

 extending laterally. (Figure 105.) Rays and skates are much 

 flattened dorsiventrally. They vary in size from the small " rugs" 

 of the New Jersey coast to large skates eight feet in diameter. 

 (Figure 106.) 



In the electric ray {torpedo-ray) modified muscle plates called 

 electropaxes are developed from the muscles of the pectoral region. 

 They are under control of the ray and connected with nerve centers 

 in the medulla. The whip-tailed or sting-rays have tails armed with 

 barbed spines, eight to nine inches long. At the base of the spines 

 poison is secreted which entering the wounds made by the tail 

 causes severe inflammation. Eagle rays may reach a width of 

 twenty feet. The animal envelops prey with its " wings." Pearl 

 divers have been drowned by these " sea vampires." Sawfish 

 may be twenty feet long with a five-foot snout equipped with saw- 

 like teeth. (Figure 107, A, B, C, D.) 



Holocephali. (Chimeras.) — The sea cat has an operculum or 

 gill cover and five claspers developed from its fins. It reaches a 

 length of three feet and rarely attacks bathers. (Figure 108). 



Subclass Elasmobranchii. Type of the Group — The Skate.^ 

 General External Characteristics. — i. Body flattened dorsiven- 

 trally. (The flounder is flattened laterally.) 



2. Pectoral fins broad, fused perfectly with head and trunk. 

 Pelvic fins well developed and bilobed, bearing claspers in the male. 



3. Ventral mouth with teeth. 



4. Paired nostrils located ventrally. 



5. Dorsally situated spiracles, originally the first pair of gill 

 clefts, communicating with the pharynx. 



6. Five pairs of gill clefts located ventrally. (Laterally in the 

 dogfish.) 



7. Ventral anus leading into cloaca. 



8. Two small pouches, one on each side of anus with two ab- 

 dominal pores opening into coelome. 



Integument.— The epidermis has several layers of cells and is 

 richly supplied with glandular goblet cells. The dermis is studded 

 with bony dermal placoid scales or " skin teeth," which are based in 



^ Since it is possible to secure rather small mature skates, many instructors prefer 

 to use them instead of the shark. We will therefore describe the skate, but present 

 figures to illustrate the nervous system of the dogfish. 



