101 



The confusion has probably arisen through Mr Adkin confound- 

 ing the hilly and mountainous districts of Perthshire, where the dark 

 forms of T. orbona do not occur, with the low-lying Moray district. 

 In Rannoch the sallows are, it is true, occasionally a few days (not 

 six weeks) later than in the low-lying districts, and the greater alti- 

 tude is quite sufficient to account for the difference ; but even then 

 Mr. Norman (" E. M. M,," vi, p. 167) records of his captures at 

 Crieff in Perthshire, where "the climate is far colder and moister 

 than in Morayshire," in 1869, as follows : — " T. gothica, March 31st, 

 common at sallows. T. stabilis, March 31st, common at sallows. 

 Scopelosoma satellitia, March 6th, common at sugar and sallows, &c." 

 Even at Crieff, then, the sallows were out on March 6th, 1869. 

 Comparing the two places — Rannoch and Moray — Mr. W. Salvage 

 writes : — " Sallows are usually out in Moray at end of March ; here 

 at Rannoch in April." But it is a fact, as I have already pointed 

 out, that in these later districts the dark forms of T. orbona do not 

 occur, whilst in the warm Moray and Sutherland districts, where 

 sallows blossom regularly at the time they do so in the south of 

 England, they do occur. What, therefore, has cold to do with the 

 melanism of T. orbona ? 



I think I have quoted sufficient authorities to show that a low 

 mean temperature does not exist in the haunts of melanic T. orbona, 

 and that the melanism of this species has an entirely different motive 

 power behind it than that of those butterflies which Mr. Merrifield 

 has shown to be affected in the direction of melanism by low tem- 

 peratures. In fact, the two phenomena, although producing a 

 similar result, viz. melanism, are brought about by entirely different 

 processes, and evidently represent results of entirely different physio- 

 logical values. 



I cannot help adding that Mr. Adkin's erroneous notion about the 

 low temperature of Scotland (a very common error, by the way) 

 would soon be dissipated were he to run over the ground and see 

 the hedges in some parts made of fuchsias, as in the warmer parts of 

 Devonshire or in the Channel Islands. 



I need not add that I shall be greatly interested to hear what Mr. 

 Adkin now considers to be the motive power in the production of 

 melanism in T. orbona. Will he not grant that certain "variational 

 units " (Weismann) of the germ are by the process of intra-selection 

 developed at the expense of the others, and that the actual pattern 

 is moulded by utility. The only influence that meteorological con- 

 ditions appear to exert in the more or less active participation in the 

 development of the more assertive variational units ? It appears to 

 me that in this, as in many other parallel circumstances in Scandi- 

 navia, Scotland, and Ireland, the excessive humidity is more likely 

 to be the prevalent meteorological factor acting on the organisms in 

 these districts. 



