ON THE VARIATION OF INSECTS. 127 



plexippus, and a similar variety occurs in nature (see ' Entomo- 

 logica Americana,' vol. i. p. 159). A noteworthy form of dichroism, 

 which must surely belong to the first division, is a change from 

 blue to red or crimson, and vice-versa. This occurs in Catocala 

 (e. g., Catocala nupta carulescens, with blue secondaries, as 

 recorded in the 'Entomologist,' p. ol), and more frequently in the 

 Locustidse, as Melanoplus atlanis cceruleipes, Ckll. ; M. packardii 

 rujipes, with hind tibiae red instead of blue (see * Canadian Ento- 

 mologist,' 1885, p. 18); Caloptenus spretus cceruleipes, with hind 

 tibiae blue instead of red (Can. Ent., 1878, 105). A similar 

 dichroism appears in the secondaries of a European locust. It is 

 worthy of remark that (so far as I know) each genus that presents 

 this kind of dichroism also has species in which yellow takes the 

 place of red or blue, and others in which the typical red varies to 

 yellow, though in these species the red does not also vary to blue, 

 nor do blue species seem to revert to yellow. Probably the yellow 

 represents least, and the blue most, specialisation, as is said to be 

 the case with the colours of flowers. 



2. This is Hagen's class 1 (Ent. Mo. Mag. 1872, 78—83). I 

 think it is almost certain that silver markings (as in Argynnis) are 

 due to a change from white, but neither white nor silver are 

 pigment. Dr. Dimmock (in ' Psyche ') compares the white to 

 ground-, and the silver to smooth-glass; and the comparison 

 seems a particularly happy one. Probably such varieties as 

 Colias edusa purpurascens belong to this division. 



3. This, in which the proportions of the different colours are 

 changed, includes a vast multitude of forms; and variation of 

 this kind, instead of being comparatively rare, like those under 

 1 and 2, occurs in almost every species. My subdivisions " m," 

 " n," " o," " p," afford good illustration of this variation. 



Additions and References. 



Glancing over the various subdivisions (" a " to " p "), I now 

 give a few addenda and references to literature, which will be 

 useful to those interested in the matter : — 



(a.) 1. I have taken a variety oi Danais plexippus, illustrating 

 a condition opposite to that of the variety of P. huntera, quoted. 

 This is described by Mr. Jenner Weir (Entom. 52). 2. See 

 Scudder, on red varieties of the locustid Amhlycorypha (' Psyche,' 

 1888, 69). I have not seen these varieties, and dare not theorise ; 

 but it is worth noting that some Locustids when put into alcohol 

 turn red. 3. The American species of Callimorpha are divided into 

 those with white and those with yellow secondaries (see Lyman, 

 Can. Entom., 1887, 181). Probably the European red-winged 

 species are more highly specialised than the American, and these 

 occasionally revert to yellow. In the same way, the American 

 form {americana) of Chelonia caia is probably nearer the primitive 



