STUDIES IN ANIMAL LIFE. 115 



come gray or yellow. In like manner species must 

 be invariable, because species is a word indicating 

 a particular group of characters ; but animals may 

 vary in these characters: they may present some 

 of the characters less or more developed, and they 

 may even want some of them. Now, as there is 

 no absolute standard of what constitutes species, 

 what sub-species, and what varieties, it becomes 

 impossible to say whether any individual variation 

 in an animal form shall constitute a new variety or 

 a new species. With regard to dogs, the differ- 

 ences between the various races are so numerous 

 and so marked as would suffice to constitute spe- 

 cies, and even genera, in other groups of animals. 



We must relinquish the idea of proving any 

 thing by the paintings and sculptures of the an- 

 cients. When we find an Egyptian plow closely 

 resembling the plow still in use in some places, we 

 may identify it as of the same " species" as our 

 own ; but this does not disprove the fact that steam- 

 plows, and plows of various construction, have 

 been since invented, all of them being modifica- 

 tions of the original type. Formerly, and for many 

 years, the stage-coach was our approved mode of 

 conveyance and it is still kept up in some dis- 

 tricts ; nevertheless, modifications of coachroad into 

 tramroad, and tramroad into railroad, have gradu- 

 ally resulted in a mode of conveyance utterly un- 

 like the stage-coach. It is the same with animals. 



Let us never forget that species have no exist- 



