92 INTRODUCTION. 



of mammalia, the conditions of the brain, and 

 showed, ,in the descending scale of its complexity 

 towards the lower organised reptilia, that the mar- 

 supials should come last, succeeding the rodentia, 

 which terminate the plancentals, and ending them- 

 selves with monotremata, who approximate to the 

 class birds in one particular, and reptilia in others.* 

 This removal from the middle of the chain, neces- 

 sitated other modifications, which, instead of leaving 

 the cetacea to the last, connects them to the carni- 

 vorous seals and morses, and passes by the herbi- 

 vorous dugongs, to the giants of the fresh waters 

 and the land, or the pachydermous order, ending in 

 the horse, and conducting us to the ruminantia, and 

 thence to the edentata and rodentia, the lowest in 

 cerebral organization, have genera which present 

 forms not unlike kangaroos. Among the marsu- 

 pials some have the characters of rodents, and might 

 connect the two sub-classes, but that it appears 

 preferable to recommence by a second series of 

 animals, from the higher organized towards the 

 lower. Thus, the first of implacentals forms the mar- 

 supialia, and the second and last order the mono- 

 tremata. But as there is every probability that all 

 the variety of forms to be found in the marsupialia 

 are by no means as yet known to naturalists, and, 



* Mr. Waterhouse, however, makes edentata the last of 

 placentals ; but Professor Owen may have had in view also 

 the condition of several rodents, who assimilate with kanga- 

 roos by the conformation of their hinder extremities, and the 

 structure of their claws. 



