SrnrUYlA M \ Kin'EHRATA I 1 :{ 



like processes known as (jill rakir.^. These appear in two rows 

 and serve to prevent food from passing throu^li tlie ^ill slits. 

 On the outer surface of each arch are numerous (jitl Jilnnuiits 

 supported by gill rays. The double row of filaments form the 

 respiratory part of the gill. Remove a portion of the first gill- 

 bearing arch and examine it in water witlj a microscope. 



If live fishes are available, study the successive respiratory 

 movements. 



There are many areas in the mouth and pharyngeal cavities 

 bearing teeth. On the upper jaw teeth are borne by the prc- 

 maxillary bones. In the center of the anterior portion of the 

 roof of the mouth are the vomerine teeth. The palatine t<'eth 

 extend obliquely caudad from the vomerine group. Further 

 caudad in the roof of the pharynx are two areas, the upper 

 pharyngeal teeth, supported by the dorsal portion of the gill 

 arches. In the lower jaw there are teeth on the dentary bones 

 which form the greater portion of the margin of this jaw. 



Three structural features of the oral and pharyngeal cavi- 

 ties of land vertebrates are lacking in fishes, namely, the 

 internal nares, the eustachian tube, and the glottis. Account for 

 their abscence. 



I'Jxtending along each side of the body and parallel with the 

 contour of the back is a line nearer the dorsal than the ventral 

 side. This is the lateral line. It consists of a row of sense organs 

 which seive to detect disturbances in the water. These sense 

 organs lie embedded in the lining of a canal found underneath 

 the line which shows at the surface and is connected with the 

 exterior by minute pores which penetrate the scales covering the 

 lateral-line canal. Remove a scale from the lateral line and 

 examine it with the microscope for a view of such a pore. 



The fins are of two types, median and paired. Of the former 

 there are two dorsals along the midline of the back, one caudal 

 (tail fin) at the caudal end of the body, and an anal fin at the 

 base of the tail on the ventral side. The paired fins correspond 

 with the fore and hind limbs of terrestrial vertebrates. The more 

 cephalic pair is known as the pectoral fins, located one on each side 

 immediately behind the operculum. The pelvic fins appear on 

 the ventral surface at a level just caudad of the pectoral fins. .Ml 

 the fins are supported l)y bony structures termed fin rays. These 

 are usually soft and flexible but may be spinelike as in the first 

 dorsal fin. 



