105 



locality are such as to render the existence of a species precarious in 

 its ordinary form and habits, but by certain possible modifications 

 its footing may be rendered more secure, will not these same local 

 conditions form the "motive power"? Humidity, temperature, 

 soil, and a multitude of other local surroundings are no doubt 

 factors in the case, but does not the whole volume of evidence that 

 has been adduced of late years on the melanic question suggest that 

 it is a complex system, rather than any one meteorological or other 

 simple power that acts on the variational susceptibilities of the 

 organism and produces these local variations ? 



Notes on the Lepidoptera observed during the Society's 

 Field Meeting at Chalfont Road on July i8th, 1896. 



Compiled by R. Adkin, F.E.S. Read July 23?-^, 1896. 



• The third field meeting of the season was held on Saturday, July 

 18th, the district selected being the Woodlands stretching along the 

 banks of the river Chess, beyond Chenies in Buckinghamshire. 

 The party, under the guidance of the president, Mr. South, left 

 Baker Street station. Metropolitan Railway, by the 2.37 train, 

 arriving at Chalfont Road about an hour later. From the station, 

 a start was made along a by-road on the left running parallel 

 with the railway. Along this road a quantity of Silene inflata grows, 

 and a nice form of Dianthmcia carpophaga has been bred from larvse 

 infesting it, but a diligent search failed to detect any of the desired 

 larvse on this occasion, although there were strong evidences of their 

 work upon some of the seed capsules, and possibly some of the 

 members, who collected quantities of the capsules at random, may 

 be rewarded by ultimately finding among them larvae that their eyes 

 were unable to detect at the time of gathering. Here, too, Pieris 

 rapce, P. napi, and P. brassiccE, which last, by-the-bye, appears to 

 have been a scarce insect during the past two or three summers, 

 were found in some numbers, and were also met with still more 

 commonly in the woods later on. Vanessa nrticce was well out, and 

 sunning itself on the scabious and thistle flowers ; while Ccenonympha 

 pamphihis, Polyonwiatus pliheas, Epmephele iafiira, and Hesperia 

 sylvanus were flying in the sunshine, and a few Streiiia clathrata and 

 Crambus pratelliis were dislodged from the herbage. 



On reaching the end of this road, a turn to the right along a 

 narrow lane brought us to the woods, their near presence being 



