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 Linnaeus. 

 Compare, for example, the Serpents among the 

 Scaly Reptiles with the Caecilians 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 



