46 GENERAL EVOLUTION. 



mental succession witnessed in animals at the present time. 

 Characters not so called now were probably as much so at one 

 period now passed. Hence embryonic characters of the bony 

 system do not, as I have often had occasion to observe, charac- 

 terize the types of the highest rank, but only subordinate divis- 

 ions of them. Thus the elasmobrauchs are j^robably repressed 

 forms of groups of a really higher gi'ade than the bony fishes, or 

 teleostei, which may be known to us. In their early presence in 

 the geologic series we have evidence of the first beginning of a 

 higher type. 



In the same manner it has been discovered that the molecular 

 aggregation of the elementary substances does not characterize 

 their highest or most distinct series, but rather the substances 

 themselves within the group or family to which they belong. 

 The gaseous, liquid, and solid molecular conditions, being charac- 

 ters distinguishing otherwise allied substances in the same way 

 morphologically (we can not say yet developmentally), as the car- 

 tilaginous, osseous, and exostosed or dermosseous characters dis- 

 tinguish otherwise nearly allied genera. 



The ''family " group embraces one or many of such series. 

 If we trace the series in several families to their simplest or most 

 generalized terms or genera, and compare them, we will not find 

 the relation to be one of exact parallelism in the series of the 

 '* order," so far as our present knowledge extends, but, in a devel- 

 opmental sense, one of divergence from the commencement. 



If we could know the simplest known terms or family charac- 

 ters of a number of groups of families, or " orders," we would 

 probably find them to represent a series of exact parallelism, 

 though to find such simplest terms we must go far into past 

 periods, since the higher the group the more extensive the range 

 of its character, and the less likely to be found unmixed with ad- 

 ditions and extensions, in modern times. 



Finally, the series of classes is in the relation of the essential 

 characters of the same, as expressed in their now extinct, most 

 generalized and simple representatives, also one of "exact paral- 

 lelism.'' 



a. Examples of Exact Parallelism.^ 



1. As an example we may take the genus Trachycephalus 

 {Batrachia anura). Nearly allied to it is the genus Osteo- 



* In generic series. 



