328 MOTIONS OF f£NSECTS. 
off the jar, when the body of 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 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 pre- 
vent them from falling. But their use will be best as- 
certained 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 di- 
stinguished by tarsi of five joints®, The grasshoppers 
with setaceous antenne (Locusta, F.) have four tarsal 
joints. Those with filiform antennse (Gryllus, F. and 
Acrydium, F.), those with ensiform (Truzalis, ¥.), and 
the crickets (Acheta, F.), have only three. In Blatta, 
the variations with respect to the suckers and cushions 
(for many species are furnished with both) are remark- 
able. The former in some (Blatta gigantea, L.) are al- 
together wanting; in others (B. Petiveriana, L.) they 
are mere rudiments; and in others (B. Madere) they 
are more conspicuous, and resemble those of the Gry/- 
lide. ‘The cushions also in some are nearly obsolete, 
and occupy the mere extremity of the four first tarsal 
joints (B. orientalis, americana, capensis, &c.). In 
B. Petiveriana there is none upon the first joint; but 
* Philos, Trans. 1816. p. 325. 
» Ina specimen in my cabinet of Blatta gigantea, the posterior 
and anterior tarsi of one side have only four joints, while the inter- 
mediate 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, 
