8 MANUAL OF NATUKAL HISTOKY. 



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 

 diad&ma). 



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 



