270 



MOVEMENT 



Insects and Arachnids. — Anions: six-les;s:ed insects 

 and eight-legged arachnids the variations in the 

 methods of progression are entirely due to the different 

 number of legs. In these species the separate legs of 

 each pair act alternately, and the movements of one 

 pair alternate with those of the next. It follows, as 

 was carefully observed by Carlet and M. de Moor,* 



Fig. 191. — Dog-fish swimming. 



that among the Coleoptera, for instance (Fig. 192), 

 the first and last appendages on the same side are 

 in contact with the ground, while the middle one is 

 raised. On the other side of the body the middle 

 appendage is on the ground, and the first and last 

 ones raised. 



When an insect turns round, the movements are 

 feebler, or cease altogether, on the side towards which 

 the animal turns. 



In the case of certain insects which jump as well as 



* De Moor (Archives de Biolojie Liege, 1890). The author gives 

 a very complete account of his studies made on the locomotion of 

 insects. He describes how he obtained the track of each of the feet 

 in different colours by coating them with different pigments; the 

 insect, as it moved, left its track on a strip of paper. He also describes 

 how he arranged the light so as to best observe the movements. 



