PREFACE xi 



which I find myself, unfortunately, somewhat at 

 variance with Professor Osborn is in the matter 

 of terminology. 



I have used the word convergence in a wide 

 sense, embracing habits, functions, structure, and 

 physiognomy ; and I venture to hope that, after 

 due consideration, this extended application will 

 prove acceptable. Under the heading "Analogy 

 in Evolution," Professor Osborn tabulates four 

 categories, namely, Analogous Variation, Paral- 

 lelism, Convergence, and Homoplasy, each of 

 which he defines. Convergence is there defined 

 as " independent similar development of un- 

 related animals, bringing them apparently closer 

 together " ; and Parallelism is " independent 

 similar development of related animals, plants, 

 and organs." 



These definitions leave us in the dark as to 

 what degrees of relationship would entitle a 

 given case to be classed as one of parallelism 

 or of convergence. The four classes represent 

 degrees of one general phenomenon, and the 

 term Analogy seems to be rather too vague 

 as applied to it. For the rest I refer the 

 reader to what I have said on the subject of 

 degrees of convergence and to the diagrams 

 of convergence and parallelism. 



Professor Gilbert C. Bourne (in the Quarterly 



