president's address. 27 



At this point, I will ask your attention for some problems whose 

 pertinency to our discussion will be evident, anda n answer to which 

 will determine our action in questions yet to be considered. 



THE EFFECT OF TEMPERATURE ON DISTRIBUTION. 



Our experimental knowledge of the influence of temperature on 

 animal life in isolated cases prepares us to find it a largely control- 

 liiig factor in the geographical distribution of the various minor 

 types, and the thermo-physiology of many super-generic types is 

 in strict consonance with their morphology. Many of the forms 

 which have been noticed as characteristic of specific realms or com- 

 mon to certain zones are limited in their range by thermometric 

 conditions. As a rule, temperature exerts a paramount influence 

 on the distribution of animal life. Nevertheless, the familiar adage 

 that there is no rule without an exception holds good for all the 

 laws of zoogeography. For instance, the tiger, which is as- 

 sociated, in the minds of most persons, with the jungles of torrid 

 India, flourishes likewise in the frigid Amurland ; the humming 

 birds, so characteristic of tropical America, are represented by 

 wanderers 'in the icy regions of both the north and south, and the 

 cyprinoid fishes live and multiply, with not greatly unequal facility, 

 in the waters of the torrid and frigid zones. Nevertheless, the rule 

 in general is that temperature is a most important factor in distri- 

 bution, and probably to its influence, in connection with the former 

 distribution of animal types and the bounds of older continents, are 

 due some of the differences which are now so salient, as, for in- 

 stance, between the North American and Eurasiatic realms. 



In former times, families now confined to America were also rep- 

 resented in Europe ; such are the Snapping turtles or Chelydrid^ 

 and the Lepidosteidse. Perhaps their present absence from the Eu- 

 ropean fauna is due to their former limitation southward, and the 

 cold of the Quaternary period, which extended over the whole of 

 their European domain and exterminated the species, while in 

 America, although the individuals over a large extent of territory 



