276 ARACHNIDES. 



ment of two small legs or palpi*, or by an appendage or lobe of 

 that same joint ; a part concealed under the mandibles, called langue 

 sternale by Savigny — description and figure of the Phalangium cop- 

 ticum — and composed of a projection in the form of a rostrum, 

 produced by the union of a very small clypeus, terminated by an 

 extremely small triangular labrum, and of an inferior longitudinal 

 carina, usually very hairy, are the parts, which, with the pieces termed 

 mandibles, constitute with some modifications the mouth of most of 

 the Arachnides. The pharynxf is placed before a sternal projection, 

 which has been considered as a lip, but which, from being placed 

 directly behind the pharynx, and having no palpi, is rather a ligula. 

 The legs, like those of Insects, are commonly terminated by two 

 hooks, and even sometimes by one more, and are all annexed to the 

 thorax, or ratlier cephalo-thorax, which except in a small number, is 

 only formed of a single segment, and is frequently intimately united 

 to the abdomen. This latter part of the body is soft, or but slightly 

 defended, in most of them. 



With respect to their nervous system, the Arachnides are greatly 

 removed from the Crustacea and Insects ; for if we except the Scor- 

 pions, which from the knots or joints forming their tail have some 

 additional ganglions, the number of these enlargements of the two 

 nervous cords is never more than three, and even in the latter, all 

 counted, it never extends beyond seven. 



Most of the Arachnides feed on Insects, Avhich they either seize 

 alive, or to which they adhere, abstracting their fluids by suction. 

 Others are parasitical, and live on vertebrated animals. Some of 

 them, however, are only found in flour, on cheese, and even on 

 various vegetables.. Those which live on other animals frequently 



* They only differ from legs, properly so called, by their tarsi, which are composed 

 of a single joint, and are usually terminated by a sniJiU hook, resembling, in a word, 

 the ordinary feet of the Crustacea. See our general observations on the first order. 



These jaws and palpi appear to correspond to the palpigerous mandibles of the 

 Decapoda, and to the two anterior feet of the Limuli. In Phalangium, the four 

 following legs have a maxillary appendage at their origin, so that these four appen- 

 dages are analogous to the four jaws of the preceding animals. I had described these 

 parts, long before the publication of Savigny's memoirs on the invertebrate animals, 

 in a monograph of the species of this genus proper to France. From these and 

 preceeding observations, it is evident that the composition of these animals is easily 

 reduced to the same general type which characterizes all articulated animals with ar- 

 ticulated feet. The Arachnides are not then a sort of acephalous Crustacea, as stated 

 by this savant, usually so exact in his anatomical observations, of which, unfortu- 

 nately for the sciences, he has become the victim. 



•f Although Savigny admits of two orifices, neither Straus nor myself can find 

 but one ; it must have been the effect of an optical illusion arising from the fact 

 of his having only perceived the lateral extremities of the fissure, its middle 

 being concealed by the tongue with which its anterior face is thickened in its mediate 

 portion. 



