APPENDIX 191 



tion of such a series of fossils as we see in the horse or the Slavonian Paludince. 

 If variations (or mutations) tend to occur more in certain particular directions 

 than in others, then unless these variants are of a disadvantageous character, 

 so as to be destroyed by natural selection, there will likely ensue a modi- 

 fication of the species in the direction of these variants. It makes no difference 

 whether or not we understand the nature and cause of such a tendency to 

 variation in particular directions; the fact that such tendencies do exist, if 

 it be a fact, must affect evolution. 



I believe that certain phenomena of paleontology and a few observations 

 of mutation indicate the existence in some species of such trends to modifica- 

 tion in particular directions. It is by no means probable that such trends 

 exist in all species. For all we know, they may arise in a species and persist 

 for a time and then disappear. We greatly need careful, extended, tabulated 

 observations upon the variation (and mutation) of many species to see if 

 variation is always fortuitous, occurring equally in all directions, or if, on the 

 other hand, the variations tend to group themselves and to be more numer- 

 ous in certain directions than in others. The observations upon (Enothera 

 lamarckiana are very suggestive, but are hardly extensive enough to give a 

 secure foundation to a theory of inherent trends in evolution. 



GERMINAL SELECTION 



Weismann, in some of his more recent writings, has urged that such trends 

 do exist, and by his theory of " germinal selection" he has endeavored to 

 explain their persistence. Weismann believes that all the organs of the adult 

 are represented in the egg and spermatozoan by minute protoplasmic par- 

 ticles which, as development proceeds, grow up each into its corresponding 

 organ. The evidence in favor of this conception is necessarily theoretical 

 more than observational, and can hardly be stated in the space at our disposal. 

 Those interested can find Weismann's own treatment of the subject in his 

 book The Germ Plasm and his essay Germinal Selection, also in his new 

 work The Evolution Theory. 



Having postulated this high degree of organization in the germ cells, each 

 part representing a particular future organ, Weismann proceeds to attribute 

 to these several determinants, as he calls them, an active struggle for food. 



