MELANISM AND MELANOCHROISM. 79 



tends to produce a large, pale variety ; while small, dark 

 specimens result from dry and stunted food. (2). Resinous, and 

 other strong vegetable properties, produce distinct brown 

 markings. (3). Chalk soils produce a chalky white or bright 

 colour in insects : conversely we should expect rich loamy 

 soils to be haunted by deeply-coloured moths. (4). A cold 

 climate, or the gloom of damp dark woods, causes a bleached 

 appearance and general absence of distinct markings." 



These conclusions are all more or less open to very serious 

 objection. In No. i, it has never been proven in the slightest 

 degree that succulent food produces pale, and dry and stunted 

 food produces dark varieties, other than in the direction I 

 have previously pointed out with regard to the relation that 

 colour bears to comparative size. This is assumed practicalh' 

 b)^ Mr. Robinson who associates " large " with "pale" and 

 " small " with " dark." Nos. 2 and 3, I consider a simple 

 outcome of the most elementary law of " natural selection,"" 

 for the dark brown colour of fir-feeding species is of the 

 utmost necessity for protection, when such species are resting 

 on the dark fir-trunk, e.g., Boannia abietaria, Retinia resinana, 

 Thera variata, and many others ; and the cause of the 

 occurrence of pallid species and varieties on chalk needs no 

 further discussion. That part of No. 4 referring to cold has 

 already been dealt with, and " bleaching and general absence 

 of distinct markings " has been provec to accompany a cold 

 climate, but the part referring to "the gloom of damp dark 

 woods " is purely theoretical and unsupported by fact, vide 

 what has been previously written concerning the Huddersfield 

 and Derby melanic varieties. 



Still continuing the discussion relative to food as a cause, 

 Mr. Cooke {Entom. x., p. 152) writes : — " The extraordinar\- 

 dark varieties in Scotland cannot have been caused by smoke 

 or chemicals, but they are, as far as my experience goes, 

 produced in black bog or peat soil, which, I suppose, contains 

 a large amount of carbon ; and this may have the same effect 

 on the caterpillars, through the tissues of the foodplants con- 

 taining more carbon than in other situations, as when the 

 caterpillars eat the carbon in the form of sopt along with their 

 food ; and again, although the country immediately around 

 York is purely agricultural, yet I am satisfied there is a 

 sufficient amount of soot deposited on the plants to affect the 

 colours of the Lepidoptera." Here again the actual fact of 

 the dark varieties being produced " in black bog or peat soil " 



