470 C. L. HUBBS 



tion of the subject, due to the increasing specialization of scientists, 

 in the lack of attention to some groups and topics (an unavoidable 

 defect in the age of specialization), and in the limited detail and 

 documentation in some of the papers. 



The diversity of treatment calls at the outset for an organized 

 indication (Table I) of the coverage of the various papers, in terms 

 of geographic, evolutionary, systematic, and background considera- 

 tions. 



The individual papers are referred to in the table (and in the fol- 

 lowing text) by number as given in the Contents. In the table, 

 degree of emphasis (in the papers as printed) is roughly approxi- 

 mated by the type: roman for least emphasis, italics, for more 

 thorough treatment, and boldface for most exhaustive coverage. 



The emphasis on background considerations and on evolutionary 

 and systematic correlatives, brought to focus in the table, is a strong 

 indication of a healthy rebound from the course of overspecializa- 

 tion. The trend toward interdisciplinary research is exemplified in 

 several of the contributions, and is perhaps best illustrated, as well 

 as stated, in Martin's contribution (15) on Pleistocene ecology. The 

 same happy trend is glowingly evident in several of the other papers, 

 notably, for example, those by MacGinitie (2) and by Blair (17). 



The overall treatment further indicates a shift from the classical, 

 purely descriptive biogeography to a kinetic approach, which is 

 more concerned with processes and explanations than with the 

 classification of the earth into a hierarchy of biogeographical regions. 

 Attention is focused on floral and faunal elements of diverse origin, 

 which may be mixed in any one area, and on the past and present 

 dispersions of these biotic elements. This concept of biotic elements, 

 which was advanced particularly by Ernst Mayr (followed herein 

 by Parkes, 16), penetrates into the limited regional classifications 

 of faunas in these symposia. Linsley (13), for example, maps the 

 same area of the central California coast as a diluted part of both the 

 Vancouveran and Californian faunas, and Rehn (12) apportions the 

 western North American orthopteran fauna according to regions 

 of origin. 



Past and continuing shifts in biota receive considerable attention, 

 in line with the more kinetic approach that is fortunately coming 

 into vogue. The background for such biotic dispersals is elucidated 

 in several of the papers, notably by King's (1) sweep through the 



