310 



COMPARATIVE ZOOLOGY. 



the animal, whose larval structure is that of a Vertebrate, 

 degenerates in its adult stage into an Invertebrate. 



DIVISION II. Acrania. 

 Vertebrates without a skull. 



CLASS. Pharyngobranchii. 



The Acrania are represented by 

 ^ the singular animal Amphioxus or 

 g Lancelet. It is about two inches long, 

 semi-transparent, without skull, limbs, 

 brain, heart, or red blood-corpuscles. 

 | It has for a skeleton a notochord only. 



I It breathes by very numerous gill 

 arches, without fringes, and the water 

 | is drawn in by cilia, which line the 

 g* gill slits. The embryo develops into 

 * a gastrula closely resembling that of 

 a the Invertebrates. The animal lives 

 >. in the sandy bottom of shallow parts 

 T,! of the ocean, and has been found in 

 g the Mediterranean Sea, in the Indian 



3 p 



i *.- Ocean, and on the east coast of North 

 ! and South America. 



a a 

 *1 



;j3 DIVISION III. Craniota. 



! - Vertebrates with a distinct skull. 

 3,1 



CLASS I. Pisces. 



t Fishes are the lowest of Verte- 



j-tj brates. They fall far behind the rest 



5.-* in strength, intelligence, and sensi- 



= bility. The eyes, though large, are 



I 1 almost immovable, bathed by no tears, 

 " and protected by no lids. Dwelling 



in the realm of silence, ears are little 



