34 
it probable that it cannot have existed in S. Louis very long 
before 1870, otherwise it would have reached the Atlantic 
sooner. We are thus driven to accept the following outline of 
its history: We know that it exists in Japan and Eastern 
Siberia; from there it must have migrated to the North Ame- 
rican Pacific Coast, perhaps long ago. It did not spread east- 
ward at once, because the necessary conditions for its existence 
were wanting on the immense plains it had to cross, just as 
the Colorado beetle lived in the Rocky Mountains on Solanam. 
rostratum, and did not spread eastwards until civilization brought 
the potato-plant (Solanwm tuberosum) with it, and thus bridged 
over for that beetle the distance between its native mountains 
and the Atlantic coast. The condition which civilization brought, 
and which favoured the rapid eastward progress of F. tenaz, 
consisted in the drains, sewers and cesspools, those necessary 
concomitants of crowded centres, and the usual abodes of the 
larva of Hristalis (1). 
Mr. F. L. Arribalzaga, in Buenos Ayres, informs me (Nov. 
1893) that this species has not been found in South America 
yet. The immigration of /. tenar into New Zealand is of a 
still more recent date than that in North America. The Cata- 
logues of the N. Z. Diptera by Nowicky (1875) and Professor 
J. W. Hutton (1881) do not mention it. It was first noticed in 
Wellington (North Island) in October and November 1888. In 
June 1890, Mr. W. W. Smith (Ashburton, South Island) writes: 
(1) All the details and references about the geographical distribution of 
JI. tenax will be found in my two articles: 
1. Facts concerning the importation or non-importation of Diptera into 
distant countries (Trans. Ent. Soe. London, 1884, p. 489—496): 
2, Some new facts concerning J’. tenaa (Entom. Monthly Mag. London, 
XXIII, p. 97—99; 1886). 
Since the appearance of J’. teraz in North America it has been discovered 
that it is already subject to the attack of a parasite. The Proctotrypid T'ro- 
pidopria comca ‘Tab. has been bred from it. (Comp. Ashmead, North American 
Proctotrypidae 1893, p. 418.) It is a European insect ,now widely distributed 
in North America and probably imported with its host.“ 
