THE FIRST ORDER OF ARACHNIDES. 



THE PULMONARL^. Unogata, Fah., 



Present, as we have already said, a vvell-marted 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 laminas. 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, when there are four, by the same arti- 

 culation of the first pair of feet, and of a tongue composed of 

 one or two 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 two), oTight to form the first genus of this 



