CYCLOSTOMATA 289 



statocyst-like sack. The brain is well developed, but lacks cere- 

 bral hemispheres and cerebellum. The ten cranial nerves are 

 of a simple type and the spinal nerves do not unite dorsal and 

 ventral roots. 



628. Class II. Pisces. The Fishes are a large group in which 

 are included animals of very diverse character. The skin is 



FIG. 169. The Devil-ray, Manta. The lateral expansions are developed 

 from the pectoral fins. This is a ventral view and shows the five pairs of gill 

 slits, the odd shaped head with the eyes on the sides of the horns, the wide, 

 straight mouth, and the whip-like tail. Taken at Beaufort, N. C. Much 

 reduced. 



usually covered with bony scales. There is a median fin which 

 may be divided into several parts. There may be one or more 

 dorsal fins, a tail fin and a ventral fin. There are usually 

 two pairs of appendages which also have the form of fins. The 

 19 



