120 
INTRODUCTION TO 
planta,') of the tarsus is frequently clothed with very 
thickly set short hairs, forming a covering, which has 
been called the foot-cushion , (pulvillus). Other pe- 
culiarities connected with this section of the leg 
will appear when we come to examine it in the dif- 
ferent orders. The number of the joints has been 
found to afford very convenient means for forming 
sub-divisions in the several primary sections, as they 
are ascertained to be pretty uniform in nearly allied 
species. Such as possess five joints in all the tarsi 
are called pentamerous ; those having five joints in 
the fore and middle legs, but only four in the hinder 
pair, heteromerous ; when all the tarsi are four 
jointed, tetramerous ; three jointed, trimerous ; two 
jointed, dimerous ; and lastly, such as have only one 
joint are termed monomerous. 
Owing to the fore legs frequently presenting a 
structure different from the rest, adapting them for 
becoming instruments of prehension, Mr. Kirby 
thought they made so near an approach to arms , 
that he applied to them that name. The five por- 
tions described above, would, in this view, be re- 
garded as analogous to the clavicle, scapula, humerus, 
cubitus, and hand. Although many remarkable 
appearances might be cited in support of this view, 
yet it is obvious that the primary use of these limbs 
as instruments of motion is never superseded, and 
we are not entitled to bestow a new name on an 
organ merely on account of a few slight modifications 
of structure, or because it has been made subservient 
to certain additional uses. It is not, besides, in all 
cases the fore legs that supply the place of arms ; in 
