250 EXPERIMENTAL EVOLUTION LECT. 



must be paid to the production of hybrids under natural 

 conditions. This study of hybridisation, scientifically 

 conducted, will certainly yield very useful results in 

 being conducive to experiments concerning that very 

 marked variability in the reproductive function which 

 in so many cases determines sterility where fertility 

 might have been expected, while fertility occurs where 

 sterility would have seemed natural. It seems that 

 the process of impregnation is of the most delicate 

 sort, and very slight circumstances slight they seem 

 at least determine its success or failure. Investi- 

 gation of these circumstances cannot but prove 

 profitable. 



Many experiments may also be performed in regard 

 to sexual and physiological selection, which are con- 

 nected with those on crossing and hybridisation, and 

 Mr. Romanes has already suggested some. 



Such are, briefly stated, the methods of experimental 

 transformism. I sincerely hope and expect that some 

 years hence, perhaps when all of us shall have become 

 things of the past, the lecturer who shall have 

 assumed the pleasant task which I here fulfil, will 

 have much more to say on this topic, and especially 

 will be able to say : " this and that have been done," 

 instead of the " this should be done " which is the 

 somewhat monotonous conclusion of each of these 

 lectures. 



