THE FIRST ORDER OF ARACHNIDES. 
THE PULMONARLE. Unogata, Fab., 
Present, as we have already said, a well-marked system of 
circulation, and pulmonary sacs, always placed under the belly, 
indicated externally by apertures or transverse clefts (stigmata), 
sometimes eight in number, four on each side, sometimes to 
the number of four or two. The number of simple eyes is 
from six to eight, while in the next order there are but four at 
most, and generally but two ; and even these are sometimes 
very little apparent, or altogether wanting. The respiratory 
organ is formed of small laminae. The heart is a large vessel 
which runs along the back, and gives out branches on each 
side, and in front. The feet are always eight in number. The 
head is invariably confounded with the thorax, and presents 
at its anterior and superior extremity two pincers or forceps 
{mandibles with some authors, cheliceres or antenne-pinces of 
Latreille), terminated by two fingers, one of which is mobile, 
or by a single one, in the form of a hook or claw, and always 
mobile. The mouth is composed of a labrum, of two palpi, 
sometimes imitating arms or talons, of two or four jaws, formed, 
when there are but two, by the radical articulation of these 
palpi ; and in addition, w hen there are four, by the same arti- 
culation of the first pair of feet, and of a tongue composed of 
one or tw r o pieces. In taking as a basis the progressive dimi- 
nution of the number of pulmonary sacs, and of stigmata, the 
scorpions, in which there are eight (while the other arachnides 
have but four or tw T o), ought to form the first genus of this 
