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 pupse of mstabilis but 

 the imagines. Instahilis hybernates as a moth not as a pupa, although 

 it hybernates within the papa 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 Tceniocampa, 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 instahilis, but I liave 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. April, 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 Nocture 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 Triana occidentalis and the European Ti'icena {Cuspidia)psi. Some- 

 times the peculiar larvte remain very similar and the moths differ in mark- 

 ing, as seems to be the case with Jocheccra fimeialis and the European 

 J. (C.) aim. 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, plecta, c-nigrum, 

 ypsilon, and fennica. The species which in America represents the 

 European A. augut, 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. — Aug. R. 

 Grote, Bremen. 



