THE YOUNG 



NATURALIST. 



37 



an apparent tendency to change may only 

 be some old characteristic reappearing. We 

 must be very careful then in taking for 

 granted that a departure from the type is a 

 step towards a new species. It may also be 

 that in some cases what we consider the 

 type is really the variety, and vice versa. 

 The grey form of Noctua neglecta is here 

 considered to be the type ; while on the 

 continent the red form, known there as 

 castanea, is considered the type, and the 

 grey form the variety. 



Varieties. 

 Varieties are those examples which differ 

 from the type in one or more directions, 

 but which occur with some degree of 

 regularity, being found either in certain 

 places where local circumstances have called 

 them into existence, and where the changed 

 form is probably advantageous to the 

 insect ; or having a range equal to that of 

 the type, and occurring with it. An 

 interesting paper by Mr. J. Jenner Weir 

 was published in the Entomologist for August 

 of last year (p. 179), in which an attempt 

 was made to classify the different kinds of 

 variation. I do not think the proposed 

 classification likely to be accepted, for 

 structural differences are mixed with 

 variations in markings, and in those classes 

 distinguished by markings only, the same 

 variety may belong to two or more. Thus 

 the dark Scotch forms of Dianthacia con- 

 spersa is given as an illustration of Melanism, 

 while it might with equal propriety be given 

 as an illustration of what the author calls 

 Topormorphism or Local Variation. He 

 also classes white, pale, and black varieties 

 as aberrations only ; yet places variable 

 species like Cidaria nissata and immanata 

 under the head of " Constant Variations." 

 Perhaps my own classification is equally 

 faulty and I shall rejoice to abandon it for 

 a better. 



In studying those species that afford the best 

 examples of Local or Permanent variation, 



' we cannot but notice the tendency of certain 

 colours to vary in given directions even when 

 the species so varying are widely separated. 

 Thus the various shades of carmine or 

 crimson have a tendency to change to 

 yellow. We have Burnets with yellow 

 hind wings and spots, Clearwings with 

 yellow bands in lieu of red, and Tigers also 

 with yellow hind wings. Orange or yellow 

 has a tendency to change to white, and this 

 obtains with insects so widely separated as 

 Venilia metadata and Chelonia plantaginis. 

 Another very noticeable thing is that the 

 same species generally become darker and 

 duller in colour towards the north and 

 lighter and brighter towards the south. 

 Most of the melanic or black forms occur in 

 the north, and while some of them are pecu- 

 liar to certain localities, others occur with 

 the type. It is probable that the duller 

 skies, and colder temperature of the North ; 

 the brighter sun and warmer climate of the 

 South are enough to account for this. A very 

 large number of the Geometrse have a dark 

 central band, and in species not possessing 

 it, varieties often occur in which it appears. 

 This is probably reversion to an ancestor of 

 very remote antiquity with banded wings, for 

 it is not likely that such a characteristic 

 should be acquired independently by so large 

 a number of widely separated species. This 

 band is formed, in varieties of bandless insects, 

 in two ways, either the other portions of the 

 wing have fewer dark scales, which are thus 

 concentrated in the band, or additional 

 dark scales are found forming it, The 

 variety conversaria of repandata is a well 

 known illustration of one, and Aversata 

 affords an example of the other. (Aversata 

 was named from the banded variety, and 

 the common form without the band, was 

 called spoliata by Dr. Staudinger in 1870). 

 Another well-marked class of variation 

 called Horeomorphism, or seasonal variation, 

 by Mr. Jenner Weir, includes those insects 

 that produce two broods in the year, with a 



