164 ( *o ) 



We know numerous cases where different individuals 

 of the same species present this relation of exact paral- 

 lelism to each other ; and as we ascribe common origin 

 to the individuals of a species, we are assured that the 

 condition of the inferior individual is, in this case, 

 simply one of repressed growth, or a failure to fulfill 

 the course accomplished by the highest. Thus, certain 

 species of the salamandrine genus amblystoma undergo 

 a metamorphosis involving several parts of the osseous 

 and circulatory systems, etc., while half grown ; others 

 delay it till fully grown ; one or two species remain in- 

 differently unchanged or changed, and breed in either 

 condition, while another species breeds unchanged, and 

 has never been known to complete a metamorphosis. 



The nature of the relation of exact parallelism is thus 

 explained to be that of checked or advanced growth of 

 individuals having a common origin. The relation of 

 inexact parallelism is readily explained as follows : With 

 a case of exact parallelism in the mind, let the repres- 

 sion producing the character of the lower, parallelize 

 the latter with a stage of the former in which a second 

 part is not quite mature : we will have a slight want of 

 correspondence between the two. The lower will be 

 immature in but one point, the incompleteness of the 

 higher being seen in two points. If we suppose the im- 

 maturity to consist in a repression at a still earlier point 

 in the history of the higher, the latter will be undevel- 

 oped in other points also : thus, the spike-horned deer 

 of South America have the horn of the second year of 

 the North American genus. They would be generically 

 identical with that stage of the latter, were it not that 

 these still possess their milk dentition at two years of age. 

 In the same way the nature of the parallelisms seen 



