( ciii ) 



farther east than Sontli India and ( 'eylon, and jirevents Profopdrcr ochus, SO 

 coiuiuon in Mexico, from cxtcndiiig sonthward beyond Venezuela ; no ocean, 

 no higli mountain-range, and no wide desert restrict Oreefa to Southern 

 Brazil and Argentina, Tlcretra capensis to South Africa, Hi/loici(s lagens and 

 allies to Central America, Hi/IoIcks cIu'i-.s/h and allies to North America (and 

 Mexico), and Celerio vespeiiillo to Central and South East Europe. The range 

 of these Sphingidae is restricted because the conditions of life (temi)erature, 

 food, com])osition of fixnna, etc.) are not suitable outside their present range. 

 It is therefore evident that tlie limits of the range of a species are determined 

 by two kinds of factors : physiograpliical barriers, beyond which the Sfjecies is 

 piiysicaily prevented from going ; and biological barriers, beyond which the 

 species is not able to exist. This lieing so, it follows that it is erroneous to 

 conclude that the limits of the range of species indicate always that a physio- 

 graphical barrier has formerly existed, that there was in the Continent or 

 the chain of Islands a discontinuity barring the way. One has to carefully 

 discriminate between those facts of geographical distribution which allow of 

 conclusions being drawn as to the former configuration of the earth's surface, 

 and tliose facts which are the result of tlie action of biological causes.* 



Since anything strange attracts more attention than the normal, it is not 

 rarely the unexpected upon whicli the student of geographical distribution lays 

 most stress, often exaggerating the significance of single cases and drawing 

 conclusions from them which are contradicted by the otlier, normal and hence 

 neglected, cases. Some small percentage of an Indian element in tlie fauna of 

 Madagascar misleads many a student to treat Madagascar as standing faunistically 

 closer to India than to Africa, and some small but conspicuous difference in the 

 fauna of Bali and Lombock, which difference is in insects not larger than that 

 between most other adjacent Malayan islands, gave rise to the famous but (in 

 Lepidoptera) arbitrary Wallacean line separating tiie Miday Arcliij>elago into a 

 western and an eastern district. Among the Sphingidae we iind a number of 

 sjiecies and genera with a ])eculiar]y striking distribution which miglit easily give 

 occasion to similarly fallacious and misleading conclusions, ('eplionodes hylas 

 consists of three subs])ecies, which occur one in Africa and Madagascar, another 

 in India, China, and Japan, and the third in tro[)ical Australia, no representative 

 being found in tlie Malay Archipelago. Celerio lineata has two subspecies in 

 file Old World : one inhabiting continental Asia, Africa, and Eurojie ; and the 

 second tropical Australia. The genus Nephele, so common in the Aethiopian 

 Region, has bnt one species each in India and the large Sunda Islands and 

 Australia. All these insects are so common that it is not likely that they have 

 been missed by the collectors in the Malay Archipelago. Further, the genus 

 Cephonodes has four species in the Malagassic Subregion, six in the Papuan 

 Subregion, and not more than two anywhere in India and the Malay Archi- 

 jiclago. Looking at such cases, the Antarctic Continent most conveniently comes 

 on the scene as a dfiis ex machina to exjilain the peculiarity in the distribution, 



* See also Xov. Xool. iii. p. .''lO.') (1S9C,). 



