8 MANUAL OF NATURAL HISTORY. 



Extremities never exceed four. Anal and oral ori- 

 fices distinct, remote, mostly at opposite extremi- 

 ties. Organs of special sense well developed, chiefly 

 situated in or near the face. Mouth with two jaws 

 opening vertically, one situated either above or be- 

 fore the other; blood, red; heart, muscular; sexes, 

 separated ; generation, viviparous or oviparous. 



MAMMALS. 



Among the many and singular forms to be met 

 with in this class, are numerous examples which 

 alike puzzle the systematist and astonish the be- 

 holder; forms which clearly prove that though linear 

 arrangements may be most convenient for our pur- 

 poses, and such they certainly are with the present 

 state of knowledge, they yet are naught but artifi- 

 cial. Some have thought circular arrangements to 

 be the natural method; but all are found imperfect, 

 unusual forms occurring, having so many apparent 

 affinities, yet with such an amount of differences 

 as to baffle the ingenuity of the most profound na- 

 turalists. A fit symbol of the arrangement of the 

 Animal Kingdom in nature might perhaps be found 

 in the beautiful web of the garden spider (Epeira 

 diadema). 



The Mammalia are placed at the head of the Ani- 

 mal Kingdom, because in them are to be found the 

 most complete development of faculties and the most 

 advanced structure. 



Man, regarded as an animal, stands first ; having 



