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 

 (Fmwes), 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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