208 STUDY OF NATURAL HISTORY. 
(143.) Of this law we have a familiar and a very 
beautiful illustration, in the annual revolution of the 
seasons ; the months of which may be compared to a 
series of beings following each other in close affinity. 
If we begin with January, we trace the gradual deve- 
lopement, first of spring, and then of summer; from 
thence we pass into autumn; this season, again, melts 
into the winter of December ; and we thus arrive 
again at the point from which we first set out. So, 
likewise, is a natural series of animals. If we begin 
at any given species or group, and trace its connec- 
tion to others, we find, that, after being conducted 
through various modifications of the original type, 
we are insensibiy brought to that type again; just 
as if, by passing the point of a pin over the figure of 
a circle, we should assuredly end where we began. 
Now, as this hypothesis has been amply verified by 
facts drawn from the animal and the vegetable 
kingdoms, it has assumed the character and the 
authority of a general law, and gives us no further 
occasion to seek upon what principle the series of 
nature is constructed. We shall have occasion, 
hereafter, to dwell more particularly on the com- 
prehensiveness of this law, and the beauty of its 
application throughout nature: at present, we merely 
point it out to the student as that basis upon which 
all his combinations must be built, and as a fixed 
- and determinate point from whence he may safely 
begin his journey onward. 
(144.) The lowest combinations of objects, wherein. 
this law can be traced, are those groups of species 
which were formerly denominated genera, but which 
are called by the moderns sub-genera,—a term in- 
