334 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



out separately before comparing results, in order that one 

 may serve to confirm or disprove the other. 



If we have read this story of the snakes correctly, there is 

 nothing in the least suggestive of an unconnected group of 

 volcanic islands thrust independently above the surface of 

 the ocean, to become the home of such animals as might reach 

 them through more or less accidental or occasional agencies of 

 dispersal. Instead of telling of the elevation of new islands, 

 the evidence points to the gradual depression and partial sub- 

 mersion of a more extensive land-mass which must have had 

 direct or indirect connection with continental America. 



When we consider the snakes from the various islands as 

 regards the style of their coloration — whether spotted or 

 striped — we find an interesting fact. On almost every island 

 only one style of coloration is present. Thus, all the snakes 

 of Hood, James, and Jervis are striped; while on Charles, 

 Albemarle, and Brattle only spotted snakes have been found. 

 But when we come to Narborough, Indefatigable and Bar- 

 rington islands, we find that each island has both spotted and 

 striped snakes. Why should a difference of coloration so 

 constant on other islands be inconstant here? 



We have seen that the snakes of Charles and of Hood are 

 alike, except that those of Charles are spotted while those of 

 Hood are striped. If these two islands should now become 

 connected for a time, we might expect spotted snakes to 

 wander to Hood, and striped ones to appear on Charles. If 

 these islands again became separated, we should find both 

 spotted and striped snakes on each island ; but if the connection 

 had been short, we might expect a majority of the snakes 

 of Charles, and a minority of those of Hood, to show the 

 spotted coloration. 



Fifty-three per cent of the fifteen snakes from Barrington 

 are spotted. Seventy-four per cent of the twenty-three speci- 

 mens from Indefatigable are striped. More numerous speci- 

 mens might change the proportion and show that the sug- 

 gested explanation is quite wrong, or that differentiation is 

 now for the first time developing between the Indefatigable 

 and the Barrington snakes. The parallelism between the con- 

 ditions actually found on Barrington and Indefatigable, and 

 the conditions which we might expect to find upon Charles 



