Tunicata. 



103 



A comparison of the Rock Dog-fish (fig. 167), with the Bass 

 (fig. 168), a bony fish, both of which are in tank No. 10, will 

 quickly reveal the essential features of the sharks and their 

 differences from the more highly- developed bony fishes. The 

 Bass is covered over its whole body with silvery fish-scales, has 

 its mouth at the anterior extremity, two large moveable gill- 



Fig. 167. Scyllium catulus, 

 Ve nat. size. 



Fig. 168. Labrax lupus, 

 */6 nat. size. 



covers, staring eyes not provided with lids, and nasal apertures 

 distinct from the mouth. The body of the Shark on the other 

 hand is not covered with scales, but with bony spines, which 

 cause the skin to feel rough. The mouth is on the under side of 

 the head in the form of a transverse slit from side to side, and 

 the neck has five or more gill-slits on each side, but no gill-cover. 

 The eyes are provided with moveable eye-lids, the nostrils com- 



