310 



COMPARATIVE ZOOLOGY. 



occipital condyles, and their blood-corpuscles are not nu- 

 cleated 158 (Mammalia). 



DIVISION I. Acrania. 



Vertebrates without a skull. 



II 



II 



fl.rf 



gla- 



SS, 8 



II! 

 Ill 



it* 



ills 



CLASS. Pharyngobranchii. 

 The Acrania are represented by 

 the singular animal Amphioxus or 

 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. 

 It breathes by very numerous gill 

 arches, without fringes, and the water 

 is drawn in by cilia, which line the 

 gill slits. The embryo develops into 

 a gastrula closely resembling that of 

 the Invertebrates. The animal lives 

 in the sandy bottom of shallow parts 

 of the ocean, and has been found in 

 the Mediterranean Sea, in the Indian 

 Ocean, and on the east coast of North 

 and South America. 



DIVISION II. Craniota. 

 Vertebrates with a distinct skull. 



CLASS I. Pisces. 



Fishes are the lowest of Verte- 

 brates. They fall far behind the rest 

 in strength, intelligence, and sensi- 

 bility. The eyes, though large, are 

 almost immovable, bathed by no tears, 

 and protected by no lids. Dwelling 

 in the realm of silence, ears are little 



