MIGRATION AND DISPERSAL OF INSECTS : ORTHOPTERA, 89 



scaled area, those of hairs to replace those of scales along the mar^^in 

 of the sensory area, if circumstances so determine. But ids or biophors 

 of sensory hairs do not become converted gradually or per mltum into 

 those of scales or rio' rfrs/i. The scales have more potency basally, the 

 hairs apically, but there is the capacity for each to completely supplant 

 the other if natural selection so decide. The capacity for further 

 evolution of sensory hairs is displayed in the diliterent forms they 

 assume, of which the sensory pit, " batonnet antennaire " of M. le 

 Professor J. Chatin,^'' appears to be the highest and most recently 

 evolved example ; but of these I do not suppose that such evolution 

 proceeds over and over again independently in the way that Dr. 

 Jordan supposes they develop into scales, but that being evolved thev 

 have great power of displacing each other if advantage accrues there"- 

 from. 



When we examine a Danaid antenna with hairs and punctures over 

 the greater part of the circumference, and with a dorsal area, forming a 

 band along the back of -the antenna, without hairs or scales, there is 

 no doubt that the sensory surfaces invaded the scale surfaces, and that 

 the scales disappeared from the remainder of the surfaces. Certainly 

 when the scales disappeared from the dorsal area, they did not at the 

 same time degenerate (or develop ?) laterally into sensory organs, but 

 were supplanted by them. There can be no doubt, since the Danaids 

 are one of the highest butterfly families that they had as ancestors 

 forms with good wide dorsal development of scales. 



The practical etiect of this view as compared with Dr. Jordan's is, to 

 deprive the Hcxjtcriiikic of the highest place, to allow that the dorsal 

 sensory area of most butterflies, and especially of Li/cacniilat', is com- 

 patible with descent from a form with dorsal scaling to the tip, and to 

 leave the Danaids near the top, while Dr. Jordan's view of the narrow 

 dorsal ai'ea only, being the only scaled portion in their ancestors, 

 would place them low down, though he does not say so. It also leaves 

 it very possible for the Hcujieriidae to be near the root of the butterfly 

 stirps, in ordinary, if not very correct expression, for the butter- 

 flies to be derived from the Hesperids. 



* " Structure et cleveloppement cles Batonnets Antennaires chez la Vanesse Paon- 

 de-Jour," par Joannes Chatin, 20 pp. and 2 pi., Paris, 1883. 



Migration and Dispersal of Insects: Orthoptera. 



By J. W. TUTT. F.E.S. 

 (Continitc'l t'nnii ji. 67.) 



We have before stated that the migratory locusts of the Old 

 World, with the exception of Scliistnrcrca pviriirina, belong to the 

 Oedijioditia". Sc/iistoccrca jiereifrina belongs to the Anidiidae, and, with 

 the exception of this insect, all the other species of the genus Sdiisto- 

 cnra are confined to America. In South America certain species of 

 this genus are migratory, one S. paranemn- is considered by many to 

 be specifically identical with S. pen-iifina. In North America a large 

 locust belonging to this genus, N. autcricana, is also migratory, but 

 Mdawiphix {('(diiptoitts) spfitiis is, undoubtedly, the chief migratory 

 species of the great northern continent. 



In North America the Rocky Mountain Locust [M. sjnrtns) appears 



