568 THE AMERICAN NATURALIST [Yol.L 



genus Scomberomorus, found in warm seas of the world. 

 Along the Atlantic coast of America S. maculatus is 

 abundant south to Florida, and 8. regalis is abundant 

 about Cuba, where maculatus is practically unknown. 

 Regalis is a close ally, we may reasonably say a deriva- 

 tive of maculatus, from which it differs in the scaling of 

 the fins, arrangement of the numerous brownish spots 

 which ornament both species, and in minor characters. 

 Occurring abundantly between the two and associated 

 with one to the north, the other to the south, is unspotted 

 8. cavalla (the kingfish of Florida), I will call such an 

 interposed species an "intrusion." Incidentally cavalla 

 is a complement of both maculatus and of regalis. 



All the above mentioned cases of variants have this in 

 common: although more or less geographical they are 

 not obvious and direct responses to the environment; 

 probably environment has little to do with them. Ap- 

 parently we get all the various types of variants as 

 classified where such control is lacking or not essential. 

 It is then pretty certain that variants occur when not 

 induced by environment. Lacking contrary evidence this 

 hypothesis is accepted, and cases where it apparently 

 obtains are alone considered in this article, environ- 

 mentally induced variants being too common and too 

 generally discussed to need treatment here. 



Let us go over the various types of variants, begin- 

 ning with the simplest, and discuss them in relation to 

 their probable origin. The admittedly inherent tendency 

 to variation in any form would be sufficient, where the 

 form is widely distributed, to break it up into adjacent 

 races. Adjacent representative species are pretty obvi- 

 ously derived from adjacent races. Even temporary 

 isolation so readily explains this slight advance and is so 

 easily assumed, that perhaps we should look no further 

 for explanation. So far we have trodden familiar 

 ground scarcely worthy of mention, and the hypothesis, 

 that namely, probably on account of competition, closely 

 related forms are antagonistic, is conservative enough. 



