389 



The above Schema is brought to an accordance with Mr. Sclatcr's 

 Schema of the geographical distribution of Birds; but in both 



schemes the calculations made as to the number of square miles to 

 one species cannot be looked upon even as attempts at approxima- 

 tions in those regions, a part of which only bas been explored 



by naturalists. Thus the large space of central A.-ia, between 250 

 and 300° W. long, and between 3.r and .">() X. lut., is quite unknown 

 — a space of about 3,000,000 square miles, which cannot be justly 

 taken into account ; and then we should have a ratio of 1 : 275,000. 

 In the /Ethiopian and Australian region, at least two-thirds of the 

 area mentioned being unknown, we should have on the average a 

 single species to 50,000 square miles for the former, and to 20,000 

 square miles for the latter region. In this way we arrive at least at 

 a more accurate idea of the series in which the regions follow one 

 another, as to their respective richness in forms : — 



1. Indian region 1 : 17,000. 



2. Australian region 1 : 20,000 (instead of 1 : G0.000). 



3. South American region 1 : 36,000. 



4. .Ethiopian region 1 : 50,000 (instead of 1 : 150,000). 



5. North American region 1 : 87,000. 



6. Palrearctic region 1 : 275,000 (instead of 1 : 350,000). 



Thus by the consideration of the geographical distribution of 

 Snakes we are obliged to acknowledge the views of the primary divi- 

 sions of the earth's surface given by Air. Sclater as those most 

 natural. I have endeavoured always to state those facts which ap- 

 parently contradict this view, as well as those which favour it ; but, 

 by stating the former, I intend rather to direct the attention of the 

 Bystematist to such less satisfying results of his exertions, than to de- 

 stroy the idea of primary ontological divisions. As, however, we do 

 not know one species of Snakes extending fully over two region-;, 

 and as we find each region occupied by a majority of peculiar genera, 

 we come to the inevitable deduction that these different forms of 

 Snakes were created in the different parts of the world where they 

 are now found ; but it would be a too precipitate inference to 

 maintain the same for all other species of the animal kingdom. 

 it I said in the beginning of this paper, Snakes form a most sta- 

 tionary tribe among animals ; but other animals are subjected to 

 internal or external agencies by which they are oecessarily spread, 

 in a longer or shorter lapse of time, beyond their primary bound- 

 aries; and it is a great mistake, in such instances, not to admit the 

 identity of species, even though it be modified into a climatic variety. 

 How tin- Batrachians are related in this respect, and what are the 



mOS( natural divisions of the earth's Mirt'aee BS U) thifl part of the 

 Reptiles will he the subject of the Second Tart of this paper. 



