102 



MAMMALIA. 



tries, where they constitute, very nearly indeed, the only mammiferous animals; but fossil 



remains of them occur, sparingly, in the ancient secondary deposits of Europe, where 



hitherto no higher MammaUa have been detected. Consequentl}^ the Marsupiata would 



appear to have been much earlier introduced upon our planet ; a further indication, if not 



of their inferiority, at least of their intrinsical separateness as a group : there is reason 



also to suspect that at former epochs they were much more numerous, as well as generally 



diffused, than at present.*] 



The first subdivision of them is distinguished by long canines, and small incisors to 



each jaw ; the back molars are beset with pointed tubercles, and the general character of 



the teeth is the same as in the 'Insectivora, which these animals entirely resemble in their 



regimen. 



The Opossums {Didelphis, Lin.), — 



Which of all the Marsupiata have been the longest known, compose a genus peculiar to America. 

 They have ten incisors above, and eight below ; three anterior compressed molars, and four sharply 

 tuberciilated back molars, the superior of which are triangular, the inferior oblong : so that, with the 

 four canines, they have in all fifty teeth, a number greater than has as yet been observed in any other 

 quadruped.f Their tongue is bristled, and the tail prehensile and in part naked ; the hinder thumb is 

 long and effectively opposable to the four other digits, whence the name Pedimana has been applied 

 to these animals ; it is not furnished with a nail. Their cvtremely wide mouth, and large naked ears, 

 give them a peculiar physiognomy. The glans penis is bifurcated. They are fetid and nocturnal 

 animals, whose gait is slow ; nestle upon trees, and there pursue birds, insects, &c., without rejecting 

 fruit : their stomach is small and simple, and the ccecum moderate and without enlargements. 



The females of certain species have a deep pouch, wherein are placed their teats, and in which the 



young are inclosed. 



The Common Opossum (D.virginiana, Pen. (fig. 41.) 

 —Nearly the size of a Cat: fur, a mixture of black 

 and white : it inhabits the whole of America, enters 

 the Tillages at night, and attacks poultry, devour- 

 ing their eggs, &c. The young at birth, sometimes 

 sLxteen in number, weigh only a grain each. Al- 

 though blind and nearly shapeless, they find the 

 nipple by instinct, and adhere until they have at- 

 timed the size of a Mouse, which happens about the 

 hftieth day, at which epoch they open their eyes, 

 riiey continue to return to the pouch until they are 

 as large as Rats. The term of uterine gestation 

 IS only twenty-six days. [Several others are known ; 

 )ne of which] the Crab-eating Opossum (D. caitcri- 

 lorus), frequents the marshes of the sea-coast, where 

 it feeds chiefly upon crabs. 



Other species possess no pouch, but merely a 

 vestige of it, or fold of skin on each side of the 

 belly. They habitually carry their young on 

 their backs, the tails of the latter being entwined 

 round that of the mother. 



[A considerable number are known, from South 

 America.] 



The Yapach {Cheironectes, Illig.j — 

 [Is merely an aquatic Opossum, with semi-pal- 

 mate toes.] 



• SiDce writirtfj the above. Prof. BlaiiiviUe has published an elabo- entertained the same idea. The question still remains sub judice; antl 



rate E-s.say on the reputed Marsupiata of the secondary deposits. it even a;»pears that tlie objections to either solution of the difficulty 



wlierein he advances the opinion that these celebrated fossil remains are more weiijhty than the arguments in its favour, 



appertain rather to reptiles of a higher organization than any now t There arc fifty-two teeth in the newly-discovered Myrtnecobitis. 



e.visting. M. Valenciennes and Prof. Owen have subsequently ad- The inultiitlication of the teeth in the Cetacea is on a different 



vocated the currently received opinion; while the first-named natu- principle.— Ed. 

 ralist has been supported by Dr. Grant, who I'uig previously had 



