IV. 



The Walk of Arthropods. 



MODERN naturalists are often reproached with their preference 

 for describing dead animals rather than for observing live ones. 

 The justice of such reproof cannot be altogether denied, and it must 

 be admitted that the knowledge of a creature's structure needs to be 

 supplemented with a knowledge of how it lives and moves before we 

 can claim to know it. Some years ago, we were much startled to 

 learn that the conventional picture of a running horse represents the 

 animal in an attitude altogether unnatural, and Muybridge's instan- 

 taneous photographs taught us how qviadrupeds really use their limbs. 

 A study of the walk of Arthropods is no less interesting, and this 

 neglected subject is dealt with in several recent papers, in the latest of 

 which Dixon (i) brings instantaneous photography to bear also on 

 the problem. 



Previous observers seem to have trusted to what they could actually 

 see of an insect's progress, or to have made it record its steps by 

 some graphic means. The most elaborate memoirs hitherto published 

 on the subject are those of Demoor (2, 3) who has studied in great 

 detail the locomotion of some insects, arachnids, and crustaceans. 

 By means of suitably arranged vertical and inclined plates of glass 

 partially covered by black paper, he compelled the creature under 

 observation to move in a straight line, as it sought or shunned the 

 light, and observed it through the uncovered glass. Beetles and 

 crustaceans were made to record their steps by walking over smoked 

 glass, and the various feet of Arthropods were dipped in different 

 colours, so that diagrams of their relative positions were obtained. 

 The horizontal and vertical displacements of the body were indicated 

 by means of a stylet attached to the abdomen. 



The ordinary method of an insect's walk seems generally agreed 

 upon ; it was long ago correctly described by Kirby and Spence. 

 The first and third legs on one side move together with the 

 second on the other, so that the creature is supported successively on 

 one of an alternate pair of tripods ; an arrangement of the highest 

 mechanical perfection, as Demoor points out. Graber (4), Carlet 

 (5), Lloyd Morgan (6), and Wilkins (7), all arrived at the same 

 diagonal scheme for the walk of an insect as that now set forth by 

 Demoor and Dixon. Demoor lays stress on the fact that each leg of 



