142 CLASS MAMMALIA. 



The tail of the Gerboas is as long, or as long and 

 half as the body. It is not very strong at its base, like that 

 of the Kanguroos. Its thickness is pretty nearly equal in 

 the entire of its extent. Sometimes it is perfectly cylin- 

 drical, at others quadrangular. It is usually covered with 

 smooth hairs to its extremity, which is terminated by a tuft 

 of long silken hairs. The Gerboas make use of their tails 

 to sustain their bodies when they rise from one leap to exe- 

 cute a new one. It then has the form of an S reversed 

 (r/2 ). M. Lepechin having cut the tails of some of these 

 animals to different degrees of length, observed that the ex- 

 tent of their leap diminished in the same proportion. Those 

 from which he cut it altogether, could not run at all, but 

 fell back directly as they attempted to raise themselves on 

 their hinder feet, wanting the necessary support of the tail. 

 The female Gerboas have eight teats placed on the whole 

 extent of the belly. The orifice of the vulva seems to be 

 confounded with the anus. The males are generally smaller 

 than the females. The tints of the skin are also less deep. 

 The genus Gerboa is now composed of several distinct 

 species, one of which is extremely abundant in Barbary, in 

 Higher and Lower Egypt, and Syria, and again in the more 

 northern climates, situated between the Tanais and the 

 Volga. 



The others occupy an immense space in Siberia and 

 the north part of Russia, from Syria to the Eastern Ocean, 

 and as far as the northern parts of Hindostan. A late one, 

 recently described by M. de Blainville, has been published, 

 though it would seem erroneously, as belonging to New 

 Holland. 



The synonymy of the Gerboas is in a very perplexing state. 

 The generality of naturalists not having observed with suf- 

 ficient care the number of toes in these animals, factitious 

 species have been the result of this inaccuracy. It will be 

 better, therefore, to reject all testimony concerning such as 



