INTRODUCTION TO DISCUSSION 65 



Diagnosis is only a provisional criterion, inasmuch as the 

 systematist would then continually seek and continually 

 suggest the search for the more fundamental tests. 



It will be argued that the true interspecific barrier 

 is not sterility but Asyngamy the cessation of inter- 

 breeding but that the first will inevitably follow, sooner 

 or later, as the incidental consequence of the second. 



Various causes of the origin of species by Asyngamy 

 will be discussed. One of these, preferential interbreed- 

 ing, may hereafter appear of the utmost significance 

 in species maintenance and species formation in the 

 higher animal sub-kingdoms. This, of course, would 

 imply that the instincts leading to preference are of 

 dominant importance. We can imagine hardly any 

 operation of Natural Selection more obvious or more 

 effective than that by which these instincts are led to 

 promote a maximum fertility. Any variation of instinct 

 causing an individual to attempt to pair outside the 

 syngamic community to which it belongs could only 

 result in a diminished representation in future genera- 

 tions. 



The consideration of a special form of Asyngamy 

 at the close of the Address leads to an unexpected result : 

 suspicion as to the validity of the generally accepted 

 interpretation of the manifold adaptations for cross- 

 fertilization. 



The conclusions set forth above, if hereafter established, 

 lead to a belief in the reality of species. Unlike and 

 apart from genera, families and other groups employed 

 in our ' little systems ' of classification which ' have their 

 day and cease to be ', not only do individuals stand out 

 as objective realities, but equally real, though far less 

 evident, are the societies into which individuals are 

 bound together in space and time by Syngamy and 

 E pigony. 



The Definition of Species by Diagnosis. 



It is now necessary to examine in some detail the most 

 usual conception of a species, a conception based upon 

 distinguishing structural characters, or Diagnosis. 



