APPENDIX A. 



GANNETS CLOSELY ALLIED TO SULA BASS AN A. 



When the present monograph was commenced it was only 

 intended to relate to Sula hassana, but it would hardly be a 

 fitting conclusion to leave off without some mention of its 

 allies of the Southern Hemisphere, S. capensis and S. serraior. 

 I have never seen these species in a state of nature, but they 

 have both been on view in the gardens of the Zoological Society 

 (London), where the}' have been kept on the Gull-pond. 

 The best marked distinction between the three Gannets is to 

 be found less in their plumage than in their geographical dis- 

 tribution. This can be defined with unusual clearness, and is 

 here shown in a map by three different kinds of shading. 

 It will be noted that these Gannets are natives of widely 

 separated portions of the globe, yet they inhabit corresponding 

 zones of latitude. It is true that the Boobies form a link, 

 but even they can hardly be said to unite the chain. If S. 

 hassana, S. capensis, and S. serrator all sprang from a common 

 ancestor, were the intervals between them once bridged over ? 

 Of the six Zoo -geographical Regions of the earth, they now 

 inhabit three. Cases of such interrupted distribution are not 

 uncommon among birds, but they are not easily accounted 

 for. The differences between Sula capensis, S. serrator, and 

 S. hassana may be stated concisely in parallel columns. 



