— 212 — 



only instance I have found in the literature consulted by me 

 concerns anotber species of Eristalis, E. anthopJiorinus Zett., 

 and that case occured in a distant and primitive country. 

 Zetterstedt, {Dipi. Scand. II, 666) being in Lapland, observed 

 a small swarm of flies of tliis species round the carcass of a 

 sheep: « Ad cadaver ovis putridissimum , aquae stagnanti 

 maximam parteni immersum, odore foetidissimum, individua 

 7 vel 8 sono pipiente celerrime circumvolando congregantia, 

 et in cadaveris parte supra aquam elevata interdum. sedentia, 

 die 16 Junii in Lapponia observavi, ova in cadavere sine 

 dubio depositura. » (1) 



In an article entitled: « Facts concerning the importation 

 or non-importation of Diptera into distant countries » (Trans. 

 Ent. Soc. London 1884, p. 489-496), I have shown that we 

 know very little about the laws which govern this class of 

 phenomena ; that importations will occur against ali probability, 

 and that, on the contrary, other importations Avhich appear 

 to US easy and probable, do not take place during centuries 

 of intercourse. Since publishing this paper, I found in Darwin's 

 « Life and Letters » voi. II, p. 243, in a letter of his to 

 J. D. Hooker, the following jD^ssage which expresses the sanie 

 idea: « Now I maintain against ali the world that no man 

 knows anything about the transoceanic power of migration » etc. 

 Without entering into the detail of this question, which is 

 foreign to my present purpose, I will merely show the very 

 interesting circumstances of the immigration of Eristalis tenax 

 into the New "World. 



The occurrence of this fly is reported from ali parts of 

 the Old "World, with the exception of South-Africa and the 

 East Indies, about which I have no certain data. It occurs in 



(Translation). In Lapland, on the 16 of Jiinc, near a very putrid carcass of a 

 sheep, the greater part of which was immersed in stagnant, most offensively smeUing 

 water, I perceived 7 or 8 specimens flying about rapidly and omitting a pipiug sound, 

 and sometimes alighting on the portion of the carcass above the water, evidently 

 for the purpose of depositing their eggs. 



