287 
But it is in the remaining two Orders of the Mammalia that 
Australia shows the greatest dissimilarity to the rest of the 
world. 
The MONOTREMATA and MARSUPIALITA, the two 
“Orders in question, comprise all the Implacental Mammalia 
known. The first of these, the MONOTREMATA, consists 
of two genera ouly.—Hehidnn _ eagle hus—the = 
(i chidna.), containing 
and the other ( Or nithon orcas of one ees udlabiatels 
Australian. The embryology and true position of these 
animals have long been a puzzle to naturalists ; but investiga- 
tions lately made “by Mr. Caldwell, Fellow of Caius College, 
Cambridge, are likely to set all doubts at rest for ever. The 
results of his labours have not yet been published, but it is 
known that he has ascertained beyond question that both 
genera are oviparous. Dr, Miklouho Macleay has also lately 
been making observations on the iserpemnit of the body of 
living Monotremata, and has found it to be extremely low for 
the class of animals to which they seem to belong, the tempera- 
ture of the Echnida being not over 85° Fahrenheit, and that of 
Ornithorhynchus about 10° less, or 75° Fahrenheit. 
The MARSUPIALIA form the main mass of the Ange 
tralian Mammalia, an Order unknown elsewhere among recent 
animals, except in the case of the DrprLparpa (Opossums) 
of North America. This Order, to judge from the Fossil 
remains, had a wide and comprehensive range over the surface 
of the earth during the period known to geologists as the 
Jurassic, and the inference therefrom is that while other 
portions of the globe have been submerged since that period, 
and re-inhabited by a later growth of living things, Australia, 
or the greater part of it, has vemained unchanged, except to 
the extent produced by extensive denudation and deep a alluvial 
or glacial deposits during countless ages. Geological discovery 
bears out this hypothesis, inasmuch as it has demonstrated the 
existence, in the filled-up cavities of the Silurian Limestone 
Rocks and the deep Pleistocene deposits found throughout 
Australia, numerous bones of Mammals of extinct species, and 
some of gigantic size, but all Marsupial. 
The existing Marsupials of Australia number a little over 
100 species, and these may be very naturally divided into five 
groups, which very faintly represent, Gr are supposed to repre- 
sent, some of the missing Orders of the Placental Mammals. 
Thus the @rass- eating Kangaroos are said to represent the U nau- 
LATA 3} the Leaf- eaters —Opossums, Flying Squirrels, &e.— 
the Roprnts ; ; the Entomaphaga, the TNSECTIVORA ; and 
the Sarcophaga, the FERA. However, these are only relations 
of analowy—ithere is no real affinity. The first of these groups, 
