30 Descent 



Smnming up the main points of these intro- 

 ductory remarks, I propose to deal with the sub- 

 jects mentioned above at some length, devoting 

 to each of them, if possible at least an entire 

 lecture. The decisive facts and discussions 

 upon which the conclusions are based will be 

 given in every case. Likewise I hope to point 

 out the weak places and the lacunae in our pres- 

 ent knowledge, and to show the way in which 

 each of you may try to contribute his part to- 

 wards the advancement of science in this sub- 

 ject. Lastly I shall try to prove that sudden 

 mutation is the normal way in which nature 

 produces new species and new varieties. These 

 mutations are more readily accessible to ob- 

 servation and experiment than the slow and 

 gradual changes surmised by Wallace and his 

 followers, which are entirely beyond our pres- 

 ent and future experience. 

 \ The theory of mutations is a starting-point 

 for direct investigation, while the general belief 

 in slow changes has held back science from such 

 investigations during half a century. 



Coming now to the subdivisions and headings 

 under which my material is to be presented, I 

 propose describing first the real nature of the 

 elementary species and retrograde varieties, 

 both in normal form and in hybridizations. A 

 discussion of other types of varieties, includ- 



