THE DIFFERENTIATION OF SPECIES. 71 



The number of scales on Indefatigable and Albemarle is the 

 same; but the specimens are at once distinguished by the 

 different coloration. The same is true for Hood and Bindloe ; 

 here we have also nearly the same number of scales, but two 

 totally different forms. The specimens from Jervis cannot be 

 distinguished from those of James ; the islands are separated 

 only eight kilometers from each other and the water is not very 

 deep between them. The same is true for Gardner and Hood, 

 which are much closer together, and separated by shallow water 

 only. The species from Albemarle, James, and Jervis, Inde- 

 fatigable, Barrington, and Charles are more closely related to 

 each other than to those of the other islands ; the species from 

 Hood, Chatham, Duncan, Bindloe, and Abingdon are more 

 distinct than those of the islands named above. 



By comparison of the number of scales it is found that the 

 greatest number of specimens of a certain island possesses a 

 number of scales which agrees with the average number of 

 scales of the specimens of the island. Out of thirty-eight 

 specimens from Barrington, for instance, twenty-one show the 

 number sixty-seven, which number represents the average 

 value ; out of thirty-six specimens from James, nineteen have 

 the average number sixty-three, and so on. 



These conditions can be shown by a graphic way. The 

 number of scales found in a lizard of a certain island, for 

 instance, Chatham, are placed on a horizontal, the number of 

 cases, corresponding to the different numbers, on a vertical, 

 line ; by uniting the points of the vertical lines a curve is 

 produced. All these curves thus constructed ascend to a 

 point, and descend on the other side. The highest point cor- 

 responds to the greatest number of cases and also to the mean 

 number of scales.^ 



What has been stated long ago for the tortoises, that they 

 are different on the different islands, is also true for the lizard 

 Tropidurus. We shall now examine the birds in this respect. 



The genus Nesomimus has been found on Indefatigable, 



^ Baur, G.: Das Variiren der Eidechsen-Gattung Tropidurus auf den Galapagos 

 Inseln. Festschrift zum siebenzigsten Geburtstage Rudolf Leuckarts. Leipzig, 

 1892, pp. 259-277. 



