ON THE ORIGIN OF GENERA. §3 



young of Trachycephalus are successively different genera, they 

 preserve most of their specifle characters so as not to be mistaken. 

 Agassiz says of the development of the North American turtles,* 

 " I do not know a turtle which does not exhibit marked specific 

 peculiarities long before its generic characters are fully devel- 

 oped." The same thing can be said of the characters of our sala- 

 manders, whose specific marks appear before their generic or even 

 family characters. I suspect that this will be found to be a uni- 

 versal law. 



It also follows, if a developmental process, as proposed, has 

 existed, that at times the change of generic type has tahen place 

 more rapidly than that of specific,] and that one and the same 

 species {if origin he the definition) has, in the natural succession, 

 existed in more than one genus. 



Apart from any question of origin, so soon as a species should 

 assume a new generic character it ceases, of course, to be specific- 

 ally the same as other individuals which have not assumed it. If 

 supposed distinctness of origin be, however, a test of specific 

 difference, we shall then have to contend with the paradox of the 

 same species belonging to two different genera at one and the 

 same time. 



It follows, therefore, in our interpretation of nature, that 

 groups defined by coloration alone are not to be regarded as genera, 

 as is done by some ornithologists and entomologists. They are 

 simply groups of species in which distinctive generic characters 

 had not appeared up to the period of reproduction. Inasmuch 

 as in development certain specific characters appear first, among 

 them part or all of the coloration pattern, it is obvious that the 

 latter do not belong to the generic category. The employment of 

 such characters, then, in this sense, is only to commence reversing 

 the terms generic and specific, and to inaugurate the process of 

 regarding each species as type of a separate genus. 



p. Of ProbaUe Cases of Transition. 



Thus the transition between the toothed and edentulous con- 

 ditions in Cetacea takes place in the ordinary growth of the indi- 

 viduals of the genus Globiocephalus, and the transition between 



* Gontrib. " N. Hist. United States," i, p. 391. Note. 



f See " Proceedings Academy," Philadelphia, 1867, p. 86, where I observe that 

 genei'ic characters are probably less inherent than specific. 



