INTERNAL AND EXTERNAL AFFINITIES. 933 
Thus, if we spoke of the relation which the bat has to 
a bird, we should term it an analogy; because between 
the two there is a vast number of intervening groups, 
but, if we compare the Ornithorhynchus with a bird, the 
resemblance is an affinity, inasmuch as no quadruped 
yet discovered shows such a decided tendency to con- 
nect these two classes of animals. The foregoing ob- 
servations may be considered as a recapitulation only of 
what has already been stated of these relations generally. 
We must now proceed to a more detailed explanation of 
the relations of affinity than has hitherto been given. 
(286.) Every object in nature has three distinct re- 
lations of affinity: one, by which it is connected with 
that object which precedes it in the scale of being; an- 
other, by which it is united to that which follows it ; 
and a third, which connects it to some other object 
placed out of its own proper circle. That these may 
be expressed with precision, we term the first two sim- 
ple or internal affinities, and the latter externadé. 
(287.) Simple or internal affinities must exist under 
any system which notices the progression of nature, 
whether the series be represented as simply linear, or 
circular: they are not, therefore, peculiar to the latter 
theory. The dog, for instance, is intermediate between 
the fox and the wolf; it has, consequently, two direct 
affinities. 
(288.) Eaternai affinities are not always so obvious 
as the former, except in those aberrant groups which 
connect two different circles; for it is manifest that if 
this third sort of affinity did not exist, the two circles 
would not blend into each other, as we see they do in 
nature. But in groups which are unusually abundant 
in species and in slight modifications of form, there is 
reason to believe that these external affinities will be 
found both in typical and aberrant circles. To give an 
instance of this. The annexed diagram explains the 
connection of two families, the shrikes (Laniade), and 
the thrushes (Merulade). Each of these is a circular 
group, their subdivisions perfectly representing each 
