Address to the British Association 203 



It appears then that much may be said in favour of that 

 direct effect of surrounding circumstances on organisms in 

 which Buffon beheved. 



Lastly, I would refer to Buffon's belief that new species 

 have arisen by degradation. This again is an opinion which, 

 after a period of disfavour, or at least of neglect, has been of 

 late revived, and has acquired considerable influence. I may 

 here refer to Anton Dohrn, who has recently advocated the 

 very widely-spread and effective action of degradation as a 

 cause of specific change. It will, I think, be generally 

 admitted that such exceptional Copepod crustaceans as 

 Tracheliastes and Lerneocera are due to degradation, and the 

 probability seems to be very strong that the Rhizocephala, 

 at least many cirripeds, and the cestoid worms, are also 

 degraded organisms. Very interesting would it be to know 

 whether existing Ascidians are also examples of degradation, 

 as not a few zoologists now suppose ; but most interesting of 

 all is that parasite of cuttlefishes, Dicyema, the structure of 

 which has been recently investigated by Professor Edward 

 Van Beneden, and made the type of a new primary division 

 of animals. Should this small worm-like organism hereafter 

 turn out to be a degraded form, it will show what an extreme 

 degree of retrograde metamorphosis may occasionally be 

 brought about. I think, then, that we have considerable 

 ground for suspecting that degradation has acted much and 

 widely in the field of Biology, and if so, Buffon is fairly 

 entitled to a certain amount of esteem on account of the 

 views he entertained with regard to it in so early a day and 

 in so undeveloped a condition of zoological science. For it 

 must not be forgotten that migration, the influence of 

 external conditions, and degradation, are connected points : 

 parts of one view. Degradation is most conspicuous under 

 violent changes of condition (such as parasitism), while migra- 

 tion only acts by bringing organisms under new conditions. 



