WHAT IS THE ORIGIN OF SPECIES? I9I 



name S. striatns Martin, are found in all parts of the world 

 and are characteristic of limestone rocks of the Eocarboniferous 

 period.* The generic characters of the specimen named Spir- 

 ifcr began to appear in Eosilurian time and continued to appear 

 till the close of Paleozoic time. The family characters, Spiri- 

 ferida;, do not date back earlier than the genus, and they con- 

 tinued to appear till the Jurassic era. The ordinal characters, 

 Telotremata, began in the Eoordovician period, and species 

 developing the ordinal characters are living at the present 

 time. The class characters, Brachiopoda, appeared among 

 the earliest Cambrian fossils, and are represented by numerous 

 species and genera in the seas of the present time, and the 

 same may be said of the branch characters, because we have 

 reached the beginning of our record. Thus it is seen that the 

 form of organism, called Spirifcr Logani, although it has been 

 extinct for millions of years, developed certain characters, 

 described as ordinal and class characters, which are still being 

 repeated in organisms now living; and although the species 

 is characteristic of the Carboniferous era, and did not appear 

 earlier or later, it developed characters (genera and family) 

 which began as early as the beginning of the Silurian, and 

 others which began in the Ordovician, and still others that 

 began as far back as our record goes. 



The Majority of the Characters of a so-called New Species have 

 Appeared Before. — When we say, then, that at a particular time 

 in geological history a new species arose, we do not mean that 

 the new species differs iii toto from its ancestors, but that a form 

 has arisen which, agreeing with them in the great majority of its 

 structural characters, yet differs from them by certain so- 

 called specific characters, their specific rank being indicated 

 by the fact that they are transmitted to their offspring with- 

 out modification. The fact of their constancy is all that dis- 

 tinguishes these characters from varietal characters ; and the 

 generic characters are like specific characters in this particular 

 of being transmitted without observable modification from 

 generation to generation. 



Theoretically, however, it is assumed that this perma- 



* See the time-scale on page 54. 



