27S pulmonarijE. 



never exceeds four, and is most generally but two ; sometimes they 

 are hardly perceptible, or even annihilated. The organ of respiration 

 is formed of little laminae. 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 confounded with 

 the thorax, and presents at its anterior superior extremity two man- 

 dibles — so called by authors, the chelicerce or antenne-pinces, Latr. 

 — terminated by two fingers, one of which is moveable, or by a single 

 one resembling a hook or claw that is always movcablef . The mouth 

 is composed of a labrumj, of two palpi, sometimes resembling arms 

 or claws, of the two or four jaws, formed, when there are but two, by 

 the radical joint of these palpi, and moreover, Avhen there are four, by 

 the same joint of the first pair of feet, and of a ligula consisting of 

 one or two pieces §. If we base our arrangement on the progressive 

 decrease of thenumber of pulmonary sacs and stigmata, the Scorpions 

 where it is eight, while in the other Arachnides it amounts to but 

 four or two, should form the first genus of this class, and consequently 

 our family of the Pedipalpi should precede that of the Araneides|f. 

 But the latter Arachnides are in a manner insulated by their male 

 organs of generation, by the claw or hook of their frontal mandibles, 

 by their pediculated abdomen and its spinning apparatus, and by their 

 habits ; besides this, the scorpions appear to form a natural transition 

 from the Arachnides Pulmonarise to the family of the Pseudo-Scor- 

 piones, or the first of the following order. We will therefore com- 

 mence, as we have said, with the Araneides or spinners. 



* According to Marsel <le Serres, Memoire surle Vaisseau Dorsale des Insectes, 

 the blood, in the Araneides and Scorpions, is first directed to the organs of respiration, 

 and thence proceeds to various parts of the body through particular vessels. Judg- 

 ing, however, from the affinity of these animals to the. Crustacea, the circulation 

 •would seem to be effected in the contrary direction. See the Memoir of Treviranus 

 on the Anatomy of Spiders and Scorpions. 



f These parts are formed of a first very large and ventricose joint, one of whose 

 superior angle?, wben the chelfe are didactyle, forms the fixed finger, and of a second 

 joint, that which forms the opposite and moveable finger or the hook, when there is 

 but one finger. In the latter case, as with several of the Crustacea, I will employ 

 the term claw. 



X See our general observations on the class. 



§. That of the Scorpions appears to be composed of four pieces, forming an elon- 

 gated and pointed triangle, directed forwards ; the two lateral ones however are 

 evidently formed by the first joint of the two anterior feet, and may be considered 

 as two jaws analogous to the first. We see by Mygale, Scorpio, &c., that the palpi 

 are divided into six joints, of which, in the other Araneides, the first or radical one, 

 is anteriorly and internally dilated to form the maxilliform lobe. Even this lobe, in 

 some species, is articulated at base, and thus becomes a maxillary appendage of this 

 same joint. Exclusive of this joint, the pulpus consists of but five, and such is the 

 most usual mode of supputation. In the Scorpions the moveable finger of the for- 

 ceps, as in that of the Crustacea, forms the sixth joint. 



II In ray Fam. Nat. du R^gne Animal, I begin with the Pedipalpi. M. Leon 

 Dufour also thinks that the Scorpions should come first. 



