47 



land, of which the skeleton here belongs to the largest 

 type, which often had a reach of fourteen feet. The 

 dodo, of which a cast of the head is shown, was a 

 large ungainly bird, resembling a hugh fledgling 

 pigeon, that became extinct on the island of Mau- 

 ritius some 250 years ago. A number of skeletons of 

 striking forms of birds are also shown here. 



Series Illustrating Geographical Distribution. — This 

 series occupies the long case in the north part of this 

 hall and the six cases east and west of it. "The laws 

 governing the distribution of animals are reducible to 

 three very simple propositions. Every species of 

 animal is found in every part of the earth having 

 conditions suitable for its maintenance, unless — 



"(a). Its individuals have been unable to reach 

 this region ? through barriers of some sort; or — 



4 '(b). Having reached it, the species is unable to 

 maintain itself, through lack of capacity for adapta- 

 tion, through severity of competition with other 

 forms, or through destructive conditions of environ- 

 ment; or — 



u (c). Having entered and maintained itself, it lias 

 become so altered in the process of adaptation as to 

 become a species distinct from the original type." — 

 (Jordan.) 



For land animals the barriers may be oceans, moun- 

 tains, large rivers, heat, and cold. The continents 



