ON THE VARIATION OF INSECTS. 147 



It is singulfir that while Triphfena comes should present such 

 remarkable varieties, — such, indeed as would warrant their being 

 called new species, could their various gradations be not traced 

 southwards to the locality of the typical comes, — yet Triplicena 

 fimbria and T. interjecta, bred from the same locality, present no 

 difference in form to the southern types. 

 The Broadway, London Fields, N.E., March 5, 1889. 



ON TflE VARIATION OF INSECTS. 



By T. D. a. Cockerell. 



(Continued from p. lOO.) 



Class II. — Varieties of Form. 



a. In the Form of the Marki?igs. 



These variations, though differing apparently from any of 

 those enumerated under Class I. (in that they are not due to a 

 change of colour, a change of structure, or necessarily a change 

 in the proportions of the colours), are probably not to be distin- 

 guished from them. The question at issue is briefly this — Do all 

 variations in the markings of insects follow the same law, differing 

 only in intensity and not in kind, or do they strike out to form 

 new patterns, different from anything which could have arisen 

 merely from an increase or decrease of the intensity of the pre- 

 existing markings ? Mr. Scudder has argued that the markings 

 on the wings of Lepidoptera arose from simple dark transverse 

 bands, which by coalescence and division, have given rise to spots, 

 streaks, and even ocelli.* Assuming a number of transverse 

 bands, which have been subject to a tendency to be interrupted at 

 intervals, it is easy to see how the wings might have become 

 ornamented with a number of equidistant spots. These spots, if 

 allowed to coalesce either in a lateral, transverse, or oblique 

 direction, or to become enlarged or suppressed, or "redistributed, 

 centripetally or centrifugally " (Darwin), will probably give us all 

 the markings that we see on the wings of insects. These spots, 

 the result of the breaking-up of the primitive bands, are well 



I seen in an American moth, Tephrosia crihrataria, Guen. Accord- 

 ing to this view, the streaked or rayed varieties (such as Spllo- 

 soma menthastri walkeri. Curt. ; S. urticcs radiata, figured by Mr. 



I C. A. Briggs (Entom. xxi. 97) ; Lyccena astrarche, var. from 

 Surrey (Entom. xii., 185, and fi^.) ; L. icarus, var. Newman, 

 Brit. Butt., 128 ; Chrysophamts phloeas, var. {tom. cit., 115) will fall 



i under Class I., " n. Coalescence of dark markings."! Staudinger, 



* See also Darwin, ' Descent of Man,' 2nd ed., pp. 428—440. 

 t The recently described Metacrias strateglca, Hudson (Entom. xxii. 5.3), probably 

 lowes the ornamentation of its fore-wings to an ancestral " radiata " variation. 



