IQ6 OYSTERS, AND ALL ABOUT THEM. 



Regarded from the former point of view, a species is 

 nothing more than a kind of animal or plant, which is dis- 

 tinctly definable from all others, by certain constant, and 

 not merely sexual, morphological peculiarities. Thus 

 horses form a species, because the group of animals to 

 which that name is applied is distinguished from all others 

 in the world by the following constantly associated charac- 

 ters. They have i. A vertebral column; 2. Mammae; 

 3. A placental embryo ; 4. Four legs ; 5. A single well- 

 developed toe in each foot provided with a hoof ; 6. A 

 bushy tail ; and 7. Callosities on the inner sides of both 

 the fore and the hind legs. The asses, again, form a 

 distinct species, because, with the same characters, as far 

 as the fifth in the above list, all asses have tufted tails, and 

 have callosities only on the inner side of the fore legs. If 

 animals were discovered having the general characters of 

 the horse, but sometimes with callosities only on the fore 

 legs, and more or less tufted tails ; or animals having the 

 general characters of the ass, but with more or less bushy 

 tails, and sometimes with callosities on both pairs of legs, 

 besides being intermediate in other respects the two 

 species would have to be merged into one. They could 

 no longer be regarded as morphologically distinct species, 

 for they would not be distinctly definable one from the 

 other. 



However bare and simple this definition of species 

 may appear to be, we confidently appeal to all practical 

 naturalists, whether zoologists, botanists, or palaeontolo- 



" What is termed stratigraphical geology is neither more nor less 

 than the anatomy of the earth ; and the history of the succession of the 

 formations is the history of a succession of such anatomies, or corre- 

 sponds with development, as distinct from generation." Professor 

 T. H. Huxley, " Geological Reform," "Lay Sermons," pp. 236-7. 



