328 MOTIONS OF INSECTS. 



the animal is suddenly brought from a state of motion 

 to a state of rest ^. This may very likely be one of their 

 uses, but there are several circumstances which mili- 

 tate against its being the only one. By their elasti- 

 city 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 (Blatia)^ the spectres (P/iasma), and the pray- 

 ing-insects (Mantis), are distinguished by tarsi of five 

 joints^. The grasshoppers with setaceous antennae (Z,o- 

 custa, F.) have four tarsal joints. Those w ith filiform 

 antenn£8 (Grj/Ilus, F. and Acrj/dium, F.), those with 

 ensiform (Ti'uj:alis,¥.), and the crickets (Acheta^F.), 

 have only three. In Blaita, the variations with re- 

 spect to the suckers and cushions (for many species 

 are furnished with both) are remarkable. The former 

 in some (Blatta giganfea, L.) are altogether wanting; 

 in others (B. Petheriana, L.) they are mere rudiments ; 

 and in others {B. Maderoe) they are more conspicuous, 

 and resemble tliose of the GryU'idce. The cushions also 

 in some are nearly obsolete, and occupy the mere ex- 

 tremity of the four first tarsal joints (i>. orientalisy 

 americana, capemis, &c.) In B. Petiveriana there is 

 none upon the first joint; but upon the extremity of 



° Philos. Trans. 1816. p. 325. 



*■ In a specimen in my cabinet of Blatla 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 an- 

 terior and intermediate tarsi have both five joints. In another specimen 

 one posterior tarsus has four and the other five joints. 



