30 
SYSTEM OF NATURE. 
animals, or at least existing only in a rudimentary state. 
Now the corpus callosum , which is the principal bond of 
union between the opposite hemispheres of the brain, had 
been regarded as the great characteristic of the brain in the 
Mammalia, and in fact this commissural apparatus presents 
the essential difference which exists between that and the 
oviparous vertebrate classes.”* When to so important a 
modification of the cerebral organ as the absence of the 
corpus callosum and septum lucidum , “ are added the 
traces of the oviparous type of structure presented in the 
circulating and absorbent systems, together with the peculi¬ 
arities of the osseous and generative apparatus, we may 
with reason suspect that distribution of the Marsupiata to 
be artificial, and founded on an imperfect knowledge of 
their mutual affinities, which from a modification of the 
teeth and extremities alone would separate and disperse the 
species amongst corresponding groups of the placental 
Mammalia.”f 
Mr. Ogilby, the talented secretary of the Zoological 
Society, has published some papers on the marsupial ani¬ 
mals in the ‘ Magazine of Natural History.’ In the course 
of his remarks he has alluded to the observations of Meck¬ 
el on the discovery of mammary glands in the female Or- 
nithorhynchus, and adds in a foot note, “ The observations 
of Meckel have been fully and most satisfactorily con¬ 
firmed, since this passage was written, by the investigations 
of Mr. Owen; and it is now definitely established that 
these singular and; anomalous animals , not only lay eggs 
and hatch them like birds , but likewise support their 
young , when excluded from the shell, by means of a thick 
milky fluid , which at that period exudes copiously from 
* Waterli. Mars. 69. 
f Owen, Phil. Trans, part i. 1837. 
