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COMPARATIVE ZOOLOGY. 
occipital condyles, and their blood-corpuscles are not nu¬ 
cleated 169 {Mammalia). 
Division I.—Acrania. 
Vertebrates without a skull. 
Class.—P haryngobranchii. 
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 
