264 



MOTIONS OF INSECTS. 



The insects of the Orthoptera order are, many of them, 

 remarkable for two kinds of appendages connected with my 

 present subject, being furnished both with suckers and 

 cushions. The former are concavo-convex processes, varying 

 in shape in different species, being sometimes orbicular, some- 

 times ovate or oblong, and often wedge-shaped, which ter- 

 minate the tarsus between the claw, one on each foot. They 

 are of a hard substance, and seem capable of free motion. 

 In some instances l , another minute cavity is discoverable at 

 the base of the concave part, similar to that in Cimbex luteal 

 The latter, the foot-cushions, are usually convex appendages, 

 of an oblong form, and often, though not always, divided in 

 the middle by a very deep longitudinal furrow, attached to 

 the under side of the tarsal joints. Sir E. Home is of opinion 

 that the object of these foot-cushions is to take off the jar 

 when the body of the animal is suddenly brought from a state 

 of motion to a state of rest. 3 This may very likely be one 

 of their uses ; but there are several circumstances which 

 militate against its being the only one. By their elasticity 

 they probably assist the insects that have them in their leaps ; 

 and when they climb they may in some degree act as suckers, 

 and prevent them from falling. But their use will be best 

 ascertained by a review of the principal genera of the order. 

 Of these the cock-roaches (Blatta), the spectres (Phasma), 

 and the praying insects (Mantis), are distinguished by tarsi 

 of five joints. 4 The grasshoppers with setaceous antennse 

 (Acrida) have four tarsal joints. Those with filiform antennse 

 (Locusta and Acrydium), those with ensiform ( Truxalis 5 ), 

 and the crickets (Gryllus), have only three. In Blatta, the 

 variations with respect to the suckers and cushions (for many 

 species are furnished with both) are remarkable. The former 



1 I observed this in the hind legs of a variety of Locusta migratoria. 



2 Philos. Trans. 1816, 325. t. xix. f. 5. 



3 Ibid. p. 325. 



4 In a specimen in my cabinet of Blatta gigantea, the posterior and anterior 

 tarsi of one side have only four joints, while the intermediate one has five. On 

 the other side the hind leg is broken off, but the anterior and intermediate tarsi 

 have both five joints. In another specimen one posterior tarsus has four and the 

 other five joints. 



b The name of this genus, properly spelled, is Troxallis, from the Greek 

 TpootaXXis, Gryllus. 



