ox THE ORIGm OF GENERA. 45 



bodies, characterized by tlieir successive relations on the lower 

 level of a subordinate range of characters. This principle is dis- 

 tinctly admitted by many zoologists,* those who deny it generally 

 failing to perceive it because they attempt to gauge a major scale 

 by characters which are really the test of one or all of the subordi- 

 nate or included scales. It holds true of most of the groups of 

 organic beings ; thus the class is a scale of orders, the order of 

 tribes. I will not now say that the tribe is a scale of families, as 

 the case is here much modified ; but what is chiefly to be consid- 

 ered in this essay is, that the family is composed of one or several 

 scales of genera. 



Second. Now, the more nearly allied genera are, the more 

 surely will these generic steps be found to fall into the direct line 

 of the steps of the development of the highest, or that with the 

 longest scale, the former being truly identical with the latter in 

 generic characters. Less allied genera will offer an inexact or in- 

 complete imitation of such identity — some additional character 

 being present to disturb it. Such genus belongs to another 

 series, characterized by the disturbing feature, whose members, 

 however, l)ear to each other the relation claimed above for such. 



The relation of genera, which are simply steps in one and the 

 same line of development, may be called exact parallelism ^ while 

 that of those where one or more characters intervene in the 

 maturity of either the lower or higher genus, to destroy identity, 

 may be called incomplete parallelism. 



The latter relation has been dwelt on by von Baer, Agassiz, and 

 other writers, but none have accepted the existence of exact paral- 

 lelism, or seen its important relation to the origin of genera. 



Third. That the lowest or most generalized terms or genera 

 of a number of allied series will stand to each other in a relation 

 of exact parallelism. That is, if we trace each series of a number, 

 up to its lowest or most generalized genus, the latter together will 

 form a series, similar in kind to each of the sub-series ; i. e., each 

 genus will be identical with the undeveloped conditions of that 

 which progresses the farthest, in respect, of course, to the char- 

 acters which define it as a series. 



Those characters of the skeleton which we are accustomed to 

 call embryonic are only so because they relate to the develop- 



* Prof. Bronn, in his " Classen u. Ordnungen des Thierreiches," has everywhere 

 a chapter on " Die aufsteigende Rcihe" ("the ascending scale"). 



