126 



A COURSE ON ZOOLOGY. 



The following table gives in resume the peculiarities 

 of the five classes of vertebrates : . 



Viviparous, suckling the young; 

 udders ; warm blood ; double and 

 complete circulation ; heart with 

 four chambers; skin ordinarily 

 covered with hair, 

 f Warm blood ; double and complete 

 I circulation ; heart with four 



chambers; feathers. 

 fCold blood; circulation double, 

 but incomplete; heart usually 

 with three cavities ; scales. 



Lungs, in the adult state; cold 

 blood; double but incomplete 

 circulation; heart with three 

 cavities ; naked skin. 



Permanent gills ; life always 

 aquatic; cold blood; circulation 

 single, but complete ; heart with 

 two cavities; scales. 



CHAPTER XIII. 

 Generalities Concerning- the Articulates. 



ALL the animals that we have so far studied, however 

 different they may be in form, structure, and habits, re- 

 semble one another in one point, their bodies all con- 

 tain a strong internal framework, to which the soft parts 

 are attached. 



There are other animals, much more numerous than 

 those in the division we have just studied, in which the 

 arrangement of soft and hard parts is exactly the oppo- 

 site of that in the vertebrates, that is, the skeleton is 

 on the outside, while the flesh and muscles are within. 



