126 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



of Amphidasys betularia, the peppered moth, which appeared near 

 Manchester, England, in 1850, and has, in parts of England and later 

 in France, completely superseded the non-melanic parent species. The 

 suggestions are: (1) The dark color matches the smoke-covered foliage 

 and affords protection against bird predation. (2) The melanic form 

 of another species has been shown to have greater viability and 

 fecundity; although untested, similar suggestions have been made for 

 doubledayaria. (3) There has been an effort to show that the melanism 

 is a result of the salts contained in the smoke-covered food of industrial 

 areas; supposedly these salts effected a permanent change in the germ 

 plasm. Unfortunately these provisional hypotheses have not been care- 

 fully and completely tested. 17 



The fish Atherina riqueti 18 has appeared in the Canal du Midi, 

 between Garonne and the Mediterranean, which has been in existence 

 only since the end of the seventeenth century. It is a fresh-water 

 derivative of the marine A. boyeri. The surviving relicts of ancient 

 forms frequently have a restricted distribution. Thus the Australian 

 lungfish, Neoceratodus jorsteri, is known only from the Burnett and 

 Mary rivers in Queensland, while its extinct relatives were widely 

 distributed; the ancient rhynchocephalian (Sphenodon) is confined 

 to New Zealand; the duckbill {Ornithorhynchus) is found only in 

 the streams of southern Australia and Tasmania; and the genus of 

 snails Pleurotomaria now occurs only in the Moluccas and Antilles. 

 Here the very barriers which limit the distribution of the forms in 

 question have conditioned their survival by keeping out more efficient 

 competitors. It must be added that a small range is not at all a neces- 

 sary characteristic of a relict form. The singular cephalopod Spirula, 

 the only one besides Nautilus with a chambered shell, ranges through 

 the Atlantic, Pacific, and Indian oceans. The genus Eukoenenia, a 

 small primitive arachnid of the order Palpigradi, has been found 

 (represented by various species) in the Mediterranean region, in 

 Texas, Siam, and Paraguay. 



Local species arise among land birds on islands, in spite of their 

 powers of flight. Such endemism may result on account of their very 

 vagility, which, combined with a homing instinct, may condition the 

 return of wandering individuals and thus increase the effectiveness of 

 their insular isolation. 19 



In contrast with the relict forms, the wide distribution of a group 

 combined with the appearance of numerous differentiations, such as 

 numerous species in a single genus, is an indication of vitality. Widely 

 distributed genera in general have numerous species. A world-wide 



