June P, l8S8.] 



SCIENTIFIC NEWS. 



539 



Natural l^i'istora)* 



THE SAND GROUSE OF TARTARY. 

 Broadly speaking we may divide migrating animals 

 into two great classes, not marked off, of course, by 

 any very hard and fast outlines. There are species, ex- 

 clusively birds, which pass regularly from tropical to 

 temperate, or from temperate to arctic climates, return- 

 ing to their original quarters at the close of the season. 

 Examples of such migrants are the swallows and the 

 nightingale, which visit us in summer, and the wild 

 goose and the fieldfare, which herald the approach of 

 winter. 



the Norwegian lemming (Myodes lentmus). At intervals 

 which may be as much as ten or fifteen years, these 

 little rodents make their appearance in the inhabited 

 and cultivated parts of Norway, moving straight to the 

 west. When they reach the ocean they plunge in and 

 swim for the Lofoten Islands, which very few only reach, 

 the majority perishing in the stormy West Fjord. 



The irruptions of the true Eastern locust (Oedipoda 

 migmtona) are well known. Occasionally this destruc- 

 tive insect enters Europe in force, and commits serious 

 damage in South Russia, Hungar}"-, and even in Ger- 

 many and France. But in these latter countries, much 

 less in Britain, it has never succeeded in establishing 

 itself in permanence. 



The Sand Grouse (Syrrhaptes paradoxus). 



The second class of migrants, much less regular in 

 their movements, include not merely birds but mammals 

 and insects. Such creatures travel in directions not 

 necessarily relating to latitude, but, as it appears to us, 

 at random, ofcen from east to west. Their expeditions 

 are not undertaken annually, nor at any regular interval. 

 They may remain for years stationary, in what we must 

 call their home, and then all at once the)' may be found 

 undertaking a distant journey. A further characteristic 

 of these irregular migrants is that they are neither known 

 to return whence they came, like the swallows, nor to 

 become naturalised in any of the countries which they 

 visit. Often indeed they may stay and breed, occurring 

 year by year in reduced numbers, and at last disappear- 

 ing altogether until a fresh immigration takes place. 



Of such irregular visitants there are instances many. 

 Naturalists have often speculated on the movements of 



In 1877 English entomologists were excited by the 

 appearance in great numbers of the "Clouded Yellow'' 

 butterfly (Colias edusa) generally considered a rarity. 

 We remember seeing these insects even in Trafalgar 

 Square, in Cavendish Square, and on the Holborn Via- 

 duct ; and near Dartford vi^e overheard a collector boast- 

 ing that he had taken " ten dozen specimens that day." 

 But in a year or two these gay visitants dwindled down 

 to their usual rank as rarities. 



We cannot, of course, further enumerate the occasional 

 migratory movements of animals, or speak of the clouds 

 of butterflies and other insects which have been seen far 

 out at sea, moving away from the nearest land. But we 

 may cast a glance at the possible causes of such wander- 

 ings. 



The most obvious is the quest for food. If a species 

 has multiplied beyond the capabilities of its normal 



