( ciii ) 



farther east tliau South India and (.'eylon, and ])revents Protopurci' ocJims, so 

 common in Mexico, from extending southward beyond Venezuela ; no ocean, 

 no high monntain-range, and no wide desert restrict Orecta to Soutliern 

 Brazil and Argentina, Tlrretra capensis to South Africa, [Ji/loictts lugens and 

 allies to Central America, Ib/loicus chersis and allies to North America (and 

 Mexico), and Cderio vespertilio to Central and South East Europe. The range 

 of these Sphinx/iflae is restricted because the conditions of life (tcmpeiature, 

 food, composition of fauna, etc.) are not suitable outside their present range. 

 It is therefore evident that the limits of tlie rang'e of a sjiecies are determined 

 by two kinds of factors : ])]iysiof;Tai)hical barriers, beyond which the species is 

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

 species is not able to exist. This being 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 theie was in the (Jontinent 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 those facts which are the result of the action of biological causes.* 



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

 rarely the unexjiected upon which the student of geographical distribution lays 

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

 conclnsions from them which are contradicted by the other, normal and hen(-e 

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

 Madagascar misleads many a student to treat Madagascar as standing faunistically 

 closer to India than to Africa, and some small but cons]iicuous ditference in the 

 fauna of Bali and Lombock, which diflerence is in insects not larger tiian that 

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

 Lepidoptera) arbitrary Wallacean line separating the M:ilay Arehijielago into a 

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

 species and genera with a peculiarly striking distribution which might easily give 

 occasion to similarly fallacious and misleading conclusions. Cephonodes Injlas 

 consists of three subspecies, which occur one in Africa and Madagascar, another 

 in India, China, and Japan, and tlie third in tropical Australia, no representative 

 being found in the Malay Archii)elago. Celi'rio linmtn has two subspecies in 

 the Old \V(]rlil : mie inhaliitiiig (■(iiitiiiental Asia, Africa, and Eiiroiie ; and tlie 

 second trojiical Australia. The genus Kcpltele, so common in the Aethiopian 

 llegion, has but one species each in India and the large Suiida 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 

 Cepltoiio<li-i( has ibur sjiecies in the Malagassic Subregion, six in the Papuan 

 Subregion, an<l not more than two anywhere in India anil the Malay Archi- 

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

 on the scene as a diuis ex machiim to explain the peculiarity in tlie distribution, 



• 8cc also Nov. Xool. Hi. p. 505 (ISOfi). 



