74 SECONDARY SERIES. 
The peculiar feature in the population of the 
whole series of secondary strata, was the preva- 
lence of numerous and gigantic forms of Saurian 
reptiles. Many of these were exclusively ma- 
rine ; others amphibious ; others were terrestrial, 
ranging in savannahs and jungles, clothed with a 
tropical vegetation, or basking on the margins of 
estuaries, lakes, and rivers. Even the air was 
tenanted by flying lizards, under the dragon 
each other's peculiar condition." With respect to the final 
cause of these peculiarities, he conjectures that they have rela- 
tion to an inferior condition of the brain and nervous system in 
the Marsupialia; and considers the more protracted period of 
viviparous utero-gestation in the higher orders of Mammalia to 
be connected with their fuller developement of the parts subser- 
vient to the sensorial functions; the more simple form, and infe- 
rior condition of the brain in Marsupialia, being attended with a 
lower degree of intelligence, and less perfect condition of the 
organs of voice. 
As this inferior condition of living Marsupialia shows this 
order to hold an intermediate place between viviparous and ovi- 
parous animals, forming, as it were, a link between Mammalia 
and Reptiles ; the analogies afforded by the occurrence of the 
more simple forms of other classes of animals in the earlier geo- 
logical deposits, would lead us to expect also that the first forms 
of Mammalia would have been Marsupial. 
In a recent letter to myself, Mr. Owen adds the following in- 
teresting particulars respecting the physiology of this remarkable 
class of animals. *' Of the generality of the law, as regards the 
simple unconvoluted form of the cerebrum in the Marsupials, I 
have had additional confirmation from recent dissections of a 
Dasyurus and Phalangista. With an organization defective in 
that part which I believe to be essential to the docility of the 
horse, and sagacity of the dog, it is natural to suppose that the 
Marsupial series of warm-blooded quadrupeds would be insuf- 
