CHAPTER XIV. 



THE ACQUIREMENT OF CHARACTERS OF GENERIC, 

 FAMILY, OR HIGHER RANK ILLUSTRATED BY A 

 STUDY OF THE BRACHIOPODS. 



IN the foregoing chapters the history of organisms has 

 been considered in its general principles. 



We have noted how organisms are, in general, different 

 for different periods of geologic time; how the peculiarities 

 of structure and function, which have led to their classifica- 

 tion into many different classes, orders, families, genera, and 

 species, are intimately associated with differing conditions of 

 environment. 



The steps by which the individual organism acquires its 

 morphological and physiological characteristics have been 

 examined, and the course of this development for each indi- 

 vidual has been found to be determined by the ancestry from 

 which it sprang. 



The principles of classification have been discussed, and 

 from the investigation in this direction it has been learned 

 that each organic individual develops in the course of its 

 individual growth not only the specific, but the generic, 

 family, ordinal, class, and branch-characters of its parents. 

 These characters have various rank in the classification ; those 

 which are of higher taxonomic rank are found to be of more 

 ancient, and those of lower rank of more recent, geological 

 origin. Therefore we may conclude, as a general law, that 

 the lower the taxonomic rank of the character the shorter has 

 been its life-period, i.e., the period of time through which it 

 has been repeated by ordinary generation. 



The various opinions regarding the nature of species have 

 been discussed. All naturalists find the employment of 

 species necessary to their science, though the exact definition 



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