PULMONARY. 323 



are hardly perceptible, or even annihilated. The organ of respira- 

 tion is formed of little lamina. The heart is a large vessel which 

 extends along the back, and gives off branches on each side and 

 anteriorly. There are always eight legs. The head is always con- 

 founded with the thorax, and presents at its anterior superior ex- 

 tremity two mandibles so called by authors, the chelicerae of La- 

 treille, terminated by two fingers, one of which is movable, or by 

 a single one resembling a hook or claw that is always movable. 

 The mouth is composed of a labrum, of two palpi, sometimes re- 

 sembling arms or claws, of the two or four jaws, formed, when there 

 are but two, by the radical joint of these palpi, and moreover, where 

 there are four, by the same joint of the first pair of feet, and of a 

 ligula consisting of one or two pieces. 



FAMILY I. 



ARANEIDES. 



This family is composed of the genus ARANEA, Lin., or the Spi- 

 ders. They have palpi resembling little feet, without a forceps at 

 the end, terminated at most by a little hook. Their frontal cheli- 

 cerae (the mandibles of authors) are terminated by a movable hook, 

 flexed inferiorly, underneath which, and near its extremity, which is 

 always pointed, is a little opening, that allows a passage to a veno- 

 mous fluid contained in a gland of the preceding joint. There are 

 never more than two jaws. The thorax usually marked with a de- 

 pression in the form of a V, indicating the space occupied by the 

 head, consists of a single segment, posteriorly to which, by means 

 of a short pedicle, is suspended a movable and usually soft abdomen; 

 it is always furnished with from four to six closely approximated 

 cylindrical or conical, articulated mamillae with fleshy extremities, 

 which are perforated with numberless small orifices for the passage of 

 silky filaments of extreme tenuity proceeding from internal reservoirs. 

 Their legs, identical as to form, but of different sizes, are composed 

 of seven joints, of which the two first form the hip, the third the 

 thigh, the fourth and fifth the tibia, and the two others the tarsus: 

 the last is terminated by two hooks usually pectinated, and in seve- 

 ral by one more, which is smaller and not dentated. The intestinal 

 canal is straight, consisting of a first stomach, composed of several 



