160 THE ENTOMOLOGIST. 



auxiliary, and in some possibly the decisive factor, in the deter- 

 mination of species. But I cannot help thinking that extravagant 

 claims have been made both as to their actual value, and per- 

 haps even more as to their comparative value with regard to 

 other structures, in dififerentiating species. Of course, if the 

 differences were such as to debar insects from pairing, no claim 

 based upon them for the differentiation of species could possibly 

 be regarded as extravagant, for the circumstance would of neces- 

 sity act automatically in keeping species apart ; and I readily 

 admit that there was a time when I was a full believer in this 

 " lock and key " theory, as it has been called, and was under the 

 impression that only the most closely connected species would 

 ever pair in a wild state, and that the fact of insects of different 

 species ever pairing (except in captivity) was in itself enough to 

 show that they were at least congeneric. But this was in the 

 days when a priori reasoning was in vogue, and when, moreover, 

 I had access to few facts other than those which entered into my 

 own very limited experience. It is now of course a matter of 

 common knowledge that scarcely any pairing, even in a wild 

 state, is out of the question, unless some obvious reason should 

 render it physically impossible ; and it would be a mere matter 

 of searching in periodicals and th-e 'Zoological Kecord' if one 

 wished to produce a long list of what would otherwise be astound- 

 ing cases. Here are a few picked up at random in the course of 

 searching for information on a widely different subject : — Tcsnio- 

 campa stahilis <? and T. gothica $ (Ent. xxi. p. 158) ; Ccrastis 

 vaccina <? and Miselia oxyacanthce ? {loc. cit. p. 188) ; XylopJiasia 

 monoglifpJui <? and Hadena trifolii ? {loc. cit. p. 282) ; MeliUea 

 athalia <? o^nd Polygonia c-album ? (Schneider, 'Iris,'xix. p. 107) ; 

 Aglais urtic(e <? and Epinephele janira ? (Ent. xxxiii. p. 224); 

 Melitcea cynthia ^ and Erehia lappona $ (Kebel, * Societasll^nto- 

 mologica,' ii. p. 73) ; Attacus cecropia 3 and Sphinx ligustri ? 

 (Ent. xix. p. 136) ; Dryas jxipliia <? and Parnassius apollo $ 

 (this I saw myself at Faido, in the Leventina, in company with Mr. 

 Warren) ; Salamis anacardii 3 and Aphelia apolUnaris ? (Trimen, 

 Proc. Ent. Soc. Lond. 1880, pp. 23, 24, the moth being a day- 

 flier, and bearing a general resemblance to the butterfly) ; Eiicldoii 

 cardamincs 3 and Bapta temerata ? (Ent. xxi. p. 188 — here there 

 is no such excuse). I have arranged these in an ascending scale 

 of significance, at least as the instances strike me, and it will be 

 readily seen that they are not the result of search, by the very 

 small number of publications mentioned. If I had the time, and 

 the search seemed sufficiently profitable, I could certainly make 

 the list several times as long, but quite enough has been said to 

 support my assertion that the differences, even between the most 

 widely separated insects of the order, are not such as to preclude 

 pairing, and therefore cannot be treated as being of the same 

 importance as if they were so. In reply to this argument it was 



