56 
THE entomologist’s RECORD. 
chiefly due to heredity, but falls, I think, into error when he advances 
the experiment as having any bearing on the conclusions of Mr. Merri- 
field, to which his experiment has led ; the fact being that Mr. Fenn 
exposed to the great cold of last winter not the pupae of instabilis but 
the imagines, histabilis hybernates as a moth not as a pupa, although 
it hybernates within the pupa case, that is, the moth is fully developed 
within the pupa case in the autumn or early winter, but does not emerge 
till the spring. I do not know how long I have been aware that this 
is the rule in T(zniocampa^ certainly for many years, and always supposed 
it was one of those things that everybody knew, and that one need not 
inquire into. It so happens that I have in recent years verified it for 
myself in the case of cruda and instabilis^ but I have not made so many 
observations as to be able to assert on my own authority that it is in- 
variable in these species or universal throughout the genus. — T. A. 
Chapman. Firbank, Hereford. Aprils 1891. 
Aneurism. — I have very little idea as to the cause of aneurism, but 
it is certainly not a rare occurrence, and is not always caused by fluid 
contained between the wing membranes. In several which I operated on 
last year, whilst the notes were appearing in the Record^ it seemed to be 
caused by an air bubble. — Wm. Reid, Pitcaple, N.B. February^ 1891. 
Representative Species of Noctu^ and the Male Genitalia. — 
It is probably generally known that in North America there are found 
certain so-called representative species of moths, which differ only in 
small details of colour, marking or structure from their European allies, 
while closely agreeing with these in form, size and habit. There can, I 
think, be no question that these representative species are related by 
blood, and that the differences, such as we find them, have resulted 
from their different environment since their separation. Sometimes 
these differences appear to be marked in the larval stage, as is the case 
with Tri(zna occidentalis 2iW<\ the European Triczna {Cuspidia) psi. Some- 
times the peculiar larvie remain very similar and the moths differ in mark- 
ing, as seems to be the case with Jocheara fu 7 ieralis and the European 
J. {C.) alni. The amount of difference is very variable ; and the limits of 
these representative species, as a class, are hardly defined. I have 
given lists of such instances as have fallen under my observation. The 
species of the genus Agrotis offer a number of such cases, and this 
genus affords also examples of identical species found in America and 
Europe. Such, for instance, appear to be A. chardinyi^ pkcta^ c-nigrmn^ 
ypsilon^ and femiica. 'The species which in America represents the 
European A. augm^ is A. haruspica^ and I select this one instance for 
the purpose of illustrating the question generally. Writers have not 
been hitherto agreed as to the constancy of the differences noted in 
marking between the two. In colour, size, and general appearance 
the two are indeed so similar that they cannot be well separated, yet it 
has been recently shown that they differ in the structure of the male 
genitalia. On the supposition that this discovery is real, it would 
certainly prove that the male genitalia are more readily susceptible of 
change than is colour, size, or marking, and that they are thus to be used 
as the basis for specific, not generic, characters. In co-existing forms, 
very closely otherwise connected, the genitalia have offered strong 
differences — an additional argument for the view here taken. — Au(J. R. 
Grote, Bremen. 
