TYPICAL AND ABERRANT GROUPS EXPLAINED. 323 
of the Annulosa, or insects. The other three divisions are 
termed aberrant, because they lead off from their own 
circle into others, and exhibit the characters of the 
typical groups under a more diminished or less_ perfect 
form. Thus, reptiles, amphibia, and fishes, are the 
aberrant, or the most imperfect divisions of the verte- 
brated animals. The barnacles (Cirripedes), the worms 
(Vermes), and the sea-worms (Annelides), are the 
aberrant divisions of the annular circle, or of insects ; 
and the swimming, wading, and gallinaceous orders hold 
the same station among birds. The aberrant groups 
of a circle, in short, are always the most imperfect of 
their kind, and are the points of connection by which 
the circle to which they belong is united to that circle 
which precedes, and to that which follows. 
(392.) The nature of the typical and aberrant divi- 
sions may be further illustrated by a more direct exam- 
ple. We will, therefore, look again to the circle of 
vertebrated animals. Quadrupeds and birds are clearly 
higher in the scale of creation than reptiles, frogs, or 
fishes: they are furnished with limbs capable of many 
uses ; their structure is more complicated, and their ana- 
tomy, although peculiar, is still more like that of man 
than what we observe in fishes and reptiles. They are, 
consequently, the two typical divisions of the vertebrate 
circle. Let us now turn to the three others. Reptiles, 
frogs, and fishes are obviously less perfect animals than 
quadrupeds or birds. They seem only to have that 
slight developement of instinct necessary to preserve and 
support existence: many of them have no feet; and 
their blood is always cold. They are nearly incapable 
of affection towards man, and have never been im- 
proved by domestication. All these circumstances tend 
to show their inferiority to birds and quadrupeds ;_ they 
are, consequently, the aberrant (or the least developed) 
groups of the five classes of vertebrated animals. The 
student cannot longer be at a loss to comprehend the 
meaning of typical and aberrant forms, groups, or 
genera, so frequently alluded to. Mr. MacLeay has gene- 
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