ANALOGOUS TYPES. . 105 
in detecting the difference between the two, so 
that he may not take the more superficial features 
as the basis of his classification, instead of those 
important ones which, though often less easily 
recognized, are more deeply rooted in the organ- 
ization. It is a difference of the same nature 
as that between affinity and analogy, to which I 
have alluded before, when speaking of the in- 
grafting of certain features of one type upon ani- 
mals of another type, thus producing a superficial 
resemblance, not truly characteristic. In the 
Reptiles, for instance, there are two groups, — 
those devoid of scales, with naked skin, laying 
numerous eggs, but hatching their young in an 
imperfect state, and the Scaly Reptiles, which lay 
comparatively few eggs, but whose young, when 
hatched, are completely developed, and undergo 
no subsequent metamorphosis. Yet, notwith- 
standing this difference in essential features of 
structure, and in the mode of reproduction and 
development, there is such an external resem- 
blance between certain animals belonging to the 
two groups that they were associated together 
even by so eminent a naturalist as Linneus. 
Compare, for example, the Serpents among the 
Scaly Reptiles with the Cecilians among the 
Naked Reptiles. They have the same elongated 
form, and are both destitute of limbs; the head 
in both is on a level with the body, without any 
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