MAMMALIA, 
102 
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 Mammalia have been detected. Consequently, 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 
tuberculated 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 extremely 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 coecum 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 villages at night, and attacks poultry, devour- 
ing their eggs, &c. The young at birth, sometimes 
sixteen 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- 
tained the size of a Mouse, which happens about the 
fiftieth day, at which epoch they open their eyes. 
They continue to return to the pouch until they are i 
as large as Rats. The term of uterine gestation i 
is only twenty-six days. [Several others are known ; 
one of which] the Crab-eating Opossum (D. cancri- i 
vorus), frequents the marshes of the sea-coast, where i 
it feeds chiefly upon crabs. 
Other species possess no pouch, but merely a i 
vestige of it, or fold of skin on each side of the jj 
belly. They habitually carry their young on j 
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.) — 
[Is merely an aquatic Opossum, with semi-pal- 
Fig. 41. — Common Opossum. l. * x / x 
mate toes.] 
• Since writing the above, Prof. Blainville has published an elabo- 
rate Essay on the reputed Marsvpiata of the secondary deposits, 
wherein he advances the opinion that these celebrated fossil remains 
appertain rather to reptiles of a higher organization than any now 
existing. M. Valenciennes and Prof. Owen have subse(iuently ad- 
vocated the currently received opinion ; while the first-named natu- 
ralist has been supported by Dr. Grant, who long previously had 
entertained the same idea. The question still remains sub judice; and 
It even appears that the objections to either solution of the difficulty 
are more weighty than the arguments in its favour. 
t There arc fifty- two teeth in the newly-discovered Myrmecohius. 
The multiplication of the teeth in the Cetacea is on a different 
principle. — E d. 
