OF WASHINGTON. 119 
where names differ ; it will bring before the eye in comparison 
species which are vicarious, which represent each other in differ- 
ent countries, although specifically distinct ; it will assist us towards 
a clearer idea as to the general habits (whether uniform or variable) 
of genera and other groups of parasites. These points, however, 
will of course be brought out in a much stronger manner by the 
tabulation of the entire records, although this present tabulation 
will assist in these directions. The table which follows, however, 
will form a record upon which to base the collection and importa- 
tion of the parasites of a destructive species an attractive idea 
which has been often discussed in entomological writings, but 
seldom carried out with much practical success. Other uses for 
such a list will unquestionably arise, and, indeed, since writing 
the introductory -lines of this paper a most striking and interesting 
instance of the value of just such knowledge, in a way the pos- 
sibility of which never even occurred to me, has been brought out 
by our fellow-member, Dr. Riley. The Hessian Fly has been 
very destructive for two years past in England, and the question 
has been, and it is an important one, whence did it come? Two 
important wheat-growing districts furnish England with niuch of 
this grain, viz., North America and Russia. Now it happens that 
within a few months of each other Dr. Riley monographed the 
North American parasites of this insect, and Dr. Lindemann 
the Russian parasites. No accurate way of fixing the source of 
the English supply was found until Dr. Riley on his recent trip 
to England discovered that the parasites there were identical with 
the Russian forms, and, with one exception, specifically distinct 
from the American forms, the exception belonging to the Russian 
fauna as well as to the American. America is thus relieved of the 
onus which falls upon Russian shoulders. 
This paper will therefore subserve several objects, and if it were 
only tolerably complete its value would be considerable. The 
record is, however, incomplete and necessarily more or less inac- 
curate. 
The European records fail in many instances to record the spe- 
cies of the host, which often, and especially in case of Aphididce 
and Coccidce, usually having wide-spread species, debars us from 
much interesting information. There, such information is usually 
recorded in connnection with treatises on the structure and habits 
