CONTINUITY. 217 



In these swarms are to be found, in small numbers, other 

 species of butterflies belonging to as many as ten different 

 genera, and even some moths; and these intruders, though 

 they structurally differ in toto from the swarms they mingle 

 with, and from one another, mimic the Heliconidea so closely 

 in colours, habits, mode of flight, &c., that it is almost im- 

 possible to distinguish the intruders from those they mingle 

 with. The obvious benefit of this mimicry is safety, the 

 intruders hence escaping detection by predatory animals. 



Mr. Bates has extended his observations to the habits of 

 life, food, variations, and geographical range of the species 

 concerned in these mimetic phenomena, and finds in every 

 case corroborative evidence of every variety and species being 

 derivative, the species being modified from place to place to 

 suit the peculiar form of Heliconidea stationed there. 



Mr. Wallace has done similar service to the derivative 

 theory by his observations and writings on the butterflies and 

 birds of the Malay Archipelago, adducing instances of 

 mimetic resemblances strictly analogous to the above ; and 

 adding in further illustration a beautiful series of instances 

 where the form of the wing of the same butterfly is so modified 

 in various islets as to produce changes in their mode of flight 

 that tend to the conservation of the variety by aiding its 

 escape when chased by birds or predacious insects. 



He has also adduced a multitude of examples of geogra- 

 phical and representative races, species, and varieties, forming 

 so graduated a series as to render it obvious that they have 

 had a common origin. 



The effect of food in the formation and segregation of 

 races and of certain groups of insects has been admirably 

 demonstrated by Mr. B. D. Walsh, of North America. 



Mr. McDonnell has been led to the discovery of a new 

 organ in electric fishes from the application of the theory 'of 

 descent, and Dr. Fritz Miiller has published numerous obser- 

 vations showing that organs of very different structure may, 

 through the operation of natural selection, acquire very similar 

 and even identical functions. Sir John Lubbock's diving 

 hymenopterous insect affords a remarkable illustration of 



