THE GENEALOGY OF SHIPS. 317 



9. Plow-crook, with share shod with a three-cornered 

 bill. Sweden, alter the last. 



10. Plow-crook, like the last, but drawn by mares or 

 cows. Sweden, after the ninth. Similar implement drawn 

 by men in ancient Egypt. Plow with metal share and 

 bent pole shown in an early manuscript of Hesiod. 



11. Common plow with share, mouldboard, beam and 

 handle. Fifty years back. 



12. Modern plow with coulter. Something very similar 

 was used in the time of Pliny. 



13. Modern plow with coulter and wheel. The same 

 was used with two wheels in the time of Pliny. 



14. Self-acting plow. Recent times. 



15. Steam plow. Recent. 



Similar fundamental relations without genetic connec- 

 tion are exemplified in series of chemical homologues, 

 where from one end to the other the contiguous terms 

 differ simply by an arithmetical common difference. Ed- 

 ward von Hartmann has directed his attention to the 

 defect in Darwinian argumentation on which I am here ani- 

 madverting.* In referring to " the ideal and the genea- 

 logical relationship of types," he says, " it would be alto- 

 gether too hasty to argue in the case of palaeontological 

 data from a simple post hoc to a propter hoc" (p. 11). The 

 relationship of types in the mineral kingdom, he says, is 

 purely ideal, not genealogical. Even in a case where the 

 transitions proceed by insensible degrees, we are not au- 

 thorized to argue, for this reason, that the successive terms 

 have a common origin ; for otherwise " one might assert 



*Von Hartmann, Wahrheit und Irrthum in Darwinisms. Eine Kritische 

 Darstellung der organischen Entwickelungstheorie. Berlin, 1875. See especially 

 pages 11, 12, 13, 15. 



