98 PHILOSOPHY OF ZOOLOGY. 
According to this view, the germs of the ferns and palms 
first expanded their leaves, and afterwards those of the sta- 
miniferous vegetables. With regard to animals, it may be 
supposed that the germs of the zoophytes only, were first 
disclosed ; afterwards those of the testaceous mollusea ; and, 
finally, those of the vertebral animals: That the organized 
beings of the first periods flourished during the continuance 
of the circumstances which were suitable to their growth ; 
and that the change which prepared the way for the evolu- 
tion of those which lived at a subsequent period, contributed 
to the extinction of the earlier races. 
According to this statement, there is little difficulty in 
accounting for the extinction and revival of the different 
races of the less perfect animals and vegetables, whose 
germs appear, even at present, to be regulated according 
to such circumstances. But it offers no solution of the 
difficulty attending the preservation of the germs of the 
more perfect animals, many of which are inseparably con- 
nected with the parent, and require the contmuance of her 
life to preserve vitality until the period of evolution. TY, 
then, the present races of quadrupeds did not exist at the 
time when the mammoth and the other extinct quadrupeds, 
whose bones Cuvier has described with so much accuracy, 
were the denizens of our plains, at what period, and under 
what peculiar physical circumstances, were they called into 
being? Is the generation of organized beings simultaneous 
or successive? Have they all been created at once; but, 
in the pregress of time, so modified by the influence of ex- 
ternal agents, as now to appear under different forms ? 
Or have they been called into being at different periods, 
according as the state of the earth became suitable for their 
reception *. The latter supposition is countenanced by 
many geological documents. 

* Sce Cuvier’s “* Recherches sur les Ossemens Fossiles de Quadrupedes,” 
1812. 9 
