III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 97 



Murray in his work on the " Geographical Distributions of 

 Mammals," p. 53, and represented in the frontispiece by 

 figures copied from Gould's " Mammals of Australia ; " but 

 instances enough for the present purpose have been already 

 quoted. 



Additional reasons for believing that similarity of struct- 

 ure is produced by other causes than merely by " Natural 

 Selection" are furnished by certain facts of zoological 

 geography, and by a similarity in the mode of variation 

 being sometimes extended to several species of a genus, or 

 even to widely-different groups ; while the restriction and the 

 limitation of such similarity are often not less remarkable. 

 Thus Mr. Wallace says, 14 as to local influence : " Larger or 

 smaller districts, or even single islands, give a special 

 character to the majority of their Papilionidae. For in- 

 stance: 1. The species of the Indian region (Sumatra, 

 Java, and Borneo) are almost invariably smaller than the 

 allied species inhabiting Celebes and the Moluccas. 2. The 

 species of New Guinea and Australia are also, though in a 

 less degree, smaller than the nearest species or varieties of 

 the Moluccas. 3. In the Moluccas themselves the species 

 of Amboyna are the largest. 4. The species of Celebes 

 equal or even surpass in size those of Amboyna. 5. The 

 species and varieties of Celebes possess a striking charac- 

 ter in the form of the anterior wings, different from that 

 of the allied species and varieties of all the surrounding 

 islands. 6. Tailed species in India or the Indian region be- 

 come tailless as they spread eastward through the Archi- 

 pelago. 7. In Amboyna and Ceram the females of several 

 species are dull-colored, while in the adjacent islands they 

 are more brilliant." Again : 1B " In Amboyna and Ceram 

 the female of the large and handsome Ornithoptera Helena 

 has a large patch on the hind- wings constantly of a pale 

 dull ochre or buff color ; while in the scarcely distinguish- 

 14 "Natural Selection," p. 167. 15 Ibid., p. 173. 



