EVIDENCES OF EVOLUTION. 99 



Hseckel's well-known monograph on the calca- 

 reous sponges shows, even in a more remarkable 

 manner, to what an extent classification depends on 

 the personal equation of the systematist, or " on his 

 predilection for lumping and splitting." In this 

 monograph the Jena professor, considering the same 

 set of forms from different points of view, offers no 

 fewer than twelve different arrangements, " among 

 which the two most nearly conventional propose 

 respectively twenty-one genera and one hundred 

 and eleven species, and thirty-nine genera and two 

 hundred and eighty-nine species." 



Similar, although less marked instances of spe- 

 cific indefiniteness are exhibited regarding the oak, 

 willow, beech, birch, chestnut, and other well-known 

 trees. It is, however, in the lowest forms of life 

 that it is most difficult to draw the line of demarca- 

 tion between one species and another, and where, 

 as all admit, the grouping of species into genera is at 

 best a matter of conjecture. The countless and com- 

 plete series of transitional forms brought up from the 

 ocean depths by the dredge and trawl are cases in 

 point. 



But more puzzling still to the systematist, are 

 those extraordinary microbian forms of life called 

 schizomycetes, which embrace the numerous micro- 

 scopic organisms known as microbes, bacteria, 



examine the question of species who has not minutely described 

 many. . . . After determining a set of forms as a distinct 

 species, tearing them up and making them separate, and then 

 making them one again (which has happened to me), I have 

 gnashed my teeth, cursed species, and asked what sin I had 

 committed to be so treated." 



