406 



THE AMERICAN NATURALIST [Vol. LI 



(brought by the same boy), one tree-rat and several thou- 

 sand field-rats. If we suppose a man to prepare a batch 

 of these rats to send them to a zoological museum, this 

 museum would most certainly receive two reddish field- 

 rats, two long-tailed ones, three house-rats, one tree-rat 

 and three normal field-rats. It stands to reason that these 

 dead rats would become five species in the museum, and 

 to anybody looking through the drawer later on, these 

 five species must look equivalent. 



By observing all kinds of rats with new characters in 

 the descendance of hybrids, we have become very skepti- 

 cal indeed in accepting as real existing species those rat 

 species which are represented by two or three skins in a 

 museum, such as, for instance, Mns Blanfordii, or Mus 

 Diardii. 



It is possible that two real species, in the sense that 

 they are real constant types, which remain constant and 

 return to constancy after a cross which heightens their 

 potential variability, not infrequently intercross, the 

 hybrids always disappearing again into the multitude of 

 tj^ical individuals of either species. 



The finding of such hybrids has undoubtedly confused 

 the species question very much ; on the one liand, several 

 hybrids or sets of hybrids of the first generation, as well 

 as '*back crosses" must have been described as species, 

 whereas, on the other hand, some naturalists, through the 

 obser\^ation of such intermediate individuals, linking the 

 types of the parental species must have come to the con- 

 clusion that they were dealing with only one varying 

 species. 



We must never forget that, though certain Rvstematists 

 may think that tlioy can divide a chest of skins, according 

 to their tn-te or oven after profound morphological or 

 ])iomot)-i('al -tudic^. into two or six or sixty species, in 

 reality tlio lK)niHlai-i('s between species in nature are far 



groups, with natural, permanent limits. 



There do exist very peculiar groui)s of animals, poly- 



