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COMPARATIVE ZOOLOGY. 



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

 cleated IM (Mammalia). 



DIVISION I. Acrania. 

 Vertebrates without a skull. 



CLASS. Pharyngobranchii. 



1*1' The Acrania are represented by 

 3 _ the singular animal Amphioxus or 

 n Lancelet. It is about two inches long, 

 jj 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 

 f gill slits. The embryo develops into 

 f a gastrula closely resembling that of 

 | the Invertebrates. The animal lives 

 ! J in the sandy bottom of shallow parts 

 .E of the ocean, and has been found in 

 ! * the Mediterranean Sea, in the Indian 

 i *- 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 

 ^J in strength, intelligence, and sensi- 

 " bility. The eyes, though large, are 

 | almost immovable, bathed by no tears, 

 s and protected by no lids. Dwelling 

 in the realm of silence, ears are little 



