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XLIII. 



PEELIMINAEY NOTE ON THE WALKING OF SOME OF THE 

 AKTHROPODA. By H. H. DIXON. 



[communicated by J. JOLY, M.A., D.SC, F.E.S.] 

 [Eead May 18, 1892.] 



Some two years ago I commenced observing the walk of some 

 insects by means of instantaneous photography ; since then I have 

 observed several flies, an earwig, a pond-skater, a cockroach, various 

 beetles, an aphis, Thysanura, caterpillars, a larva of a beetle, several 

 spiders and scorpions. In these observations I used a quarter- 

 plate camera with instantaneous shutter, set looking vertically 

 down on the animal, which walked on a horizontal white ground. 

 I found it necessary to take these photographs in sunlight 

 in order that the shadows cast by the legs might show if these 

 were in contact with the ground or not. In some cases where 

 the animal experimented on showed a tendency to run into the 

 corners of the box which was used to confine it, I found it a 

 good plan to place the creature on a sheet of white paper floating 

 in a shallow dish of water, thus confining it without casting any 

 shadow on the space in which it moved. 



In all the adult Arthropoda which I have examined (except 

 the Thysanura), I find that almost simultaneous motion of the 

 " diagonals " is the rule ; that is, the Hexapods move the first and 

 third leg on one side with the second leg on the other, while the 

 Arachnida move the first and third on one side with the second 

 and fourth on the other. 



However, this apparently simultaneous motion is shown by 

 instantaneous photography not to be absolutely synchronous ; thus 

 in the blow-flies photographed the most posterior leg of the set 

 of diagonals, which seems to move together, really is raised from 



