PACKARD] THE LOCUSTS OF THE OLD WORLD. 655 



even in couutiies very northern; tbns. it was observed in England (1093 and 1748), 

 and even at the latter date, near Edinburgh; in Sweilen (as far as Ostidgoth), 

 at latitude riT'^toCB'^ north, in 1748 and 1844, and iJnally on the Duna, near Dunabourg 

 and at Polczk, in irj45. But these troops of voyagers did not hatch out in the sauio 

 placed where they were observed, nor did they leave any progeny in subsequent years. 

 The only known example of an exception to this rule is the discovery made once by 

 Boheman, in September, in the middle of Sweden, of a Pachytylus migratoriua in the 

 proper state. Eviilently this is an exception wholly accidental, which does not prove 

 anything against the rule. The more we advance toward the north, the less are large 

 swarms of locusts observed, and we end by meeting only isolated individuals, as have 

 been seen several times at St. Petersburg, and even near Wasa in Finland (latitude 

 e-J'^ north). 



The want of facts prevents onr extending these studies to the southern boundary of 

 the area of distribution of Pachytylus mUjratorius. However, we can remark that in 

 New Zealand, the extreme southern point of this distribution, the mean temperature 

 of the warmer months is, according to Schmid (Lehrbuch der Meteorologie, p. ;5G3), at 

 15^.5 R. (about 66° Fahrenheit), \\hich does not ditier muck from the corresponding 

 temperature of the northern'limit of the area in Europe. 



The localities out of Europe where the Pachytylus migratoriiis has been observed are 

 as follows : Madeira, Algeria, Tunis, Egypt, Chaitoum, Asia Minor, Syria, Arabia, Per- 

 sia, India, Siam, China, Japan, Java, Lufon, Fid-schi, New Caledonia, New Zealand, 

 Northern Australia, and 6nally Mauritius island; but this last locality indicated by 

 Serville needs confirmation. In Central Asia the species has been observed near Lake 

 Aral, on the borders of Syr-Darja, on the u|)per side of Ischim and of Irtisch, and 

 finally toward the lakes Kurgaldschin, Nor-Saisan, and Balchaasch. 



According to M. Koppen, the great chains of mountains are a powerful obstacle to 

 the diffusion of Pachytylus inujraiorius. The Alps especially play a large part in its dis- 

 tribution in Europe, and it is without doubt to them that we should attribute its rela- 

 tive rarity in the countries of the southwest of Europe and northwest of Africa, where 

 it is almost completely replaced by other species of the same group,!. e.,the Culoptcnus 

 italica in Spain, Italy, and in the middle of France ; the Acrydium pengrinum in Algeria. 



It should be observed that this species, and in general all the Acrydiidcc, shun mount- 

 ainous and wooded countries. They are most fond of the plains, of regions quite dry, 

 and it is also a circumstance which influences necessarily their geographical distribu- 

 tion. 



"The development of the organs of flight of the migratory locust," continues M. Kop- 

 pen, " determines the facility and the amplitude of its flight, and consequently favors 

 its migrations. Thty are evidently the cause of this coiotsal geographical disliibution 

 of the species. They remind us ( f the remark of Darwin, that species rich in individ- 

 uals and with a wide habitat, which, owing to their organization, have had in their 

 country the pre-eminence over many surrounding sjiecies, are those which, in the case 

 of emigrations cut of their area, should have the greater chances of overrunning new 

 territories." 



Koppen examines successively the causes which may determine the migrations of 

 this orthopter in armies more or less numerous, and then the observed direction of these 

 movements. It is said that they fly more often from east to west, but M. Koppen 

 thinks that it is not necessary to attribute this circumstance, as has been done, to the 

 predominance of the east winds at times when the sterility of the country that they 

 inhabit, iucreased still by the prevalence of these same winds, forces them to seek 

 places which can furnish them a more abundant pasturage. Numerous facts appear, 

 be says, to contradict this explanation. In reality, the movements of these hordes is 

 rather ce-ntri(ngal, as M. Kiippen establishes from observations made especially in the 

 plains of Eastern Europe; that is to say, that all the migrations ai)pear to radiate 

 irora countries where the species breeds most. In Europe they would consequently be 

 diiected to the west, while in China they should have a direction ordinarily toward 

 the southeast, 



M. Koppen thinks that the same centrifugal radiation has presided over the scatter- 

 ing of this species beyond its original limits, atid that this radiation, propagating in 

 waves, such as we still see produced at the liniits of its geographical area, has carried 

 the species from its center of creation or its original country to points where it is 

 powerless to overcome the climatic conditions or that concurrence of vital forces which 

 are opposed to it. The center of creation or the point of departure of the species will 

 be found, then, in Central Asia. The complete absence of thisspecies on the American 

 continent shows that it only began to exist as a species after the epoch of the separa- 

 tion of America from the Old World. 



M. Prudhomme de Bone adds, "In this study, so interesting, there is one point ou 

 which we should insist. It is this, that the observations of M. Koppen tend to confirm 

 the principle of zoological geography, that the area of a 8j)ecieB cannot be limited on 

 the map by a simple curve, but between places where the sjtecies exist in a constant or 

 normal manner and those where its absence is constant there is always a zone, often 



