96 



rsrcHE. 



Jul)'— August iSSS. 



stroy an\'thing on their journey but go harm- 

 lessly along. Fowls will not eat them and 

 birds do not appear to molest them." 



Mr. Lint;on identifies the species, with 

 some doubt, as the common Polydcsin/ts ery- 

 ihropygii!'. Science, I3july i88S, v. 12, no. 

 284, p. 24. 



Riverside Natural History. — Under 

 this title Messrs. Houghton, Mifflin and com- 

 pany have issued a newedition of The Stan- 

 dard Natural History (S. E. Cassino & 

 Co.). The insects occupy nearly five hun- 

 dred pages of the second volume and with 

 the exception of an appendix by Dr. Packard, 

 and a bibliography. of some of the more im- 

 portant publications bj' Mr. Woodworth, the 

 text of the two editions is unchanged. Dr. 

 Packard's contribution consists of a brief 

 account of the Thysanopfera {T/irips and 

 allies). The bibliography would have been 

 more useful if some arrangement (either 

 alphabetical or chronological) had been fol- 

 lowed. Two plates, a swarm of May-flies and 

 the Hercules beetle originally printed plain 

 are given in color; they are taken from 

 Brehm's Thierlebeii as are a large number of 

 the figures. No credit is given in either of 

 the editions for any of the illustrations; this 

 is a mistake from every point of view. It is 

 as important for the editors and publishers to 

 show, as it is for the neophyte to know, that 

 the illustrations are from eminent authorities. 



On melanism in Lepidoftera. — A cas- 

 ual observation this spring led me to form a 

 hypothesis as to the cause and meaning of 

 melanism in Lepidoptera, which appears to 

 explain a considerable majority of the in- 

 stances, and at the same time, correlates vari- 

 ous fi\cts in connection with it, that are other- 

 wise of obscure import. I am not sufficientlv 

 acquainted with the literature of the subject 

 to know whether the same hypothesis has 

 been advanced before, but I do not happen to 

 have met with it. Melanism appears to be a 

 western rather than a northern form of vari- 

 ation, to be associated with a wet rather than 

 with a cold climate; and it hascertainly been 



more common of recent years, which maybe 

 attril:)uted to the long succession (unprece- 

 dentetl) of wet seasons we have recently 

 passed through. My obscrxation was on 

 D\^i/ir/iea'\ fagella. Twenty j'ears ago this 

 species afforded here an occasional dark or 

 even black x'ar. Happening to meet with 

 one of these, I searched carefully for two 

 seasons, ])ut only got one black and two dark 

 specimens. For the last year or two (result 

 of wet seasons) they have been fairlj' numer- 

 ous. Visiting certain oak trees with a lan- 

 tern one night lately, and the same observa- 

 tion might, occasion favoring, no doubt 

 have been made during the dav, I found the 

 dark var. quite numerous, about one to three 

 of the ordinary form. The point I wish 

 to call attention to is this : the afternoon 

 had been showery, and one side of the trunk 

 was very wet, the other dry, the wet side was 

 of a very dark color, the dry portions pale, 

 and, as a consequence the dark specimens of 

 Vh^ fagella were very conspicuous on the dry 

 portions, hardly visible on the wet, whilst 

 with the ordinary form the conditions were 

 reversed, those on the wet bark were conspic- 

 uous, those on the dry much less so. This 

 observation appears to admit of generalising, 

 because we know that many trunks of trees, 

 rocks, stones, mosses, iJcc. are much darker 

 in color when wet, the change often being 

 from pale grey to black, and that most of the 

 species that are subject to melanic variation 

 are such as are in the habit of resting on such 

 objects; natural selection would thus have 

 abundant leverage to work with. I do not 

 know whether the melanism of the Lanca- 

 shire and Yorkshire districts is acknowledged 

 to depend on the general griminess of all 

 natural objects, trees, stones, &c., but tiiere 

 is no doubt that this blackness of the resting 

 places of insects is intensified when they are 

 wet. This hypothesis will not probably ex- 

 plain all cases of melanism, but it seems to 

 be widely applicable. — T. A. Chapman, in 

 Ent. mo. niag.]\\\y iSSS, v. 25, p. 40. 



No. 146 was issued SJune 1SS8. 



