664 
VERTEBRATA. 
KANCfAKQOS. 
I 
ORDER 13. MARSTJPIALIA OR MARSUPIATA.* 
This order derives its name from marsupium, tlie Latin for purse or bag, the females of the sev- 
eral species which constitute it having under the belly a pouch or sac, in which the young, which 
are born in a very immature state, are received and nourished, and whither 'they retreat long after 
they are able to move about. The physiology as well as the osseous structure of all these ani- 
mals must of course be adapted to this most carious system; but in other- respects they vary 
greatly in size, form, and habits. The species are mostly confined to Australia, that strange quar- 
ter of the globe, where cherry-stones grow on the outside of the pulp ; where the big end of a 
pear is attached to the stalk ; where nettles, ferns, and grasses grow into trees, and lilies, tulips, and 
honeysucMes assume almost the substantial form of oaks. Before the discovery of New Holland, 
the Europeans had become acquainted with the opossum in America, and we may conceive their 
* Some naturalists divide the Mammalia into two groups, the Fkicmtar'm and Aplacentuna. In order to show 
the reason of this, it is necessary to say that it is well established that in the prod'uctian, or, more properly, the re- 
production of life, vegetable as well as animal, it is necessary that the Germ-cell and the Sperm-cell should combine, 
the principle of growth being in the hitter, and communicated to tlie former by this union, in which the germ-cell is 
penetrated by the filaments of tlie spei'm-cell. The germ-cell in the mammalia is the simplest form of what we call 
an Ovum or Ugg, provided by the oviary of the female ; this being fecundated by the sperm-cell, is brought into the 
uterus, where it gradually grows iuto the living being Avhich, at the proper time, is born. During this process of 
growth, it is connected with the womb by the Placenta^ and througli tliis it maintains its connection with the mother 
and obtains nutriment for its support and growth. The animals thus nursed by means of the placenta, are all brought 
to a state of greater or less maturity before birth, and hence those subject to this system are called Placerttaria. In 
this division all the animals noticed in the preceding pages are included. But we are now about to examine another 
division, the Marsnpiata, in which, though the origin of reproduction is the same as we have described, the young, 
instead of being nursed to maturity by means of a placenta, are brought forth while yet in embryo, and are nursed 
in a pouch situated on the abdomen of the mother. These are called Aplacentarm. It is apparent that this system of 
reproduction somew?jat apjjroaches that of birds and reptiles, in which the ovum or egg itself is produced and then 
hatched, usually by incubation. As we might expect from such a circvimstance, the aplacentia are generally of a lower 
grade of intelligence than other mammalia. 
