Class 2. 



Div. 3. ARTICULATA.— ARACHNIDA. 



451 



by a pectoral elongation ; two maxillae, formed of the basal joint of two small feet 

 or palpi *, or of an appendage or lobe of the same joint ; a piece concealed beneath 

 the mandibles, and caUed the sternal tongue by Savigny in Phalangium copticum, 

 and which is composed of a beak-like prominence, produced by the union of a very 

 small epistome or clypeus, terminated by a very small triangular upper lip, and of 

 a longitudinal lower rib (carene) generally very hairy. These, together with the pieces 

 called the mandibles, generally constitute, with certain modifications, the mouth of the 

 majority of the Arachnida. The pharynxf is placed in front of a sternal prominence, 

 which has been considered as a hp, but which, from its situation immediately in front 

 of the pharynx, and from being destitute of palpi, is rather a tongue. The legs, like 

 those of the Insecta, are generally terminated by two small hooks (ungues) and 

 sometimes by an additional one, and aU are annexed to the thorax (or rather 

 cephalo thorax), which, except in a few species, is only composed of a single piece, 

 and very often intimately united to the abdomen, which is soft or but weakly 

 defended in the majority. 



With respect to their nervous system, the arachnida remarkably differ from the 

 Crustacea and Insecta, for, if we except the Scorpions, which, in consequence of 

 their articulated tails, have some extra ganglions, the number of these knots does 

 not exceed three, and even in those animals there are only seven. 



The majority of the Arachnida feed upon insects, which they seize ahve, or upon 

 which they fix themselves, and from which they suck their juices. Others live as 

 parasites upon the bodies of vertebrated animals. There are, however, some which 

 are found only in flour, cheese, and upon various vegetables. Those which sub- 

 sist upon other animals often increase in a very great degree. In some species two 

 of the legs are not developed before a change of skin, and in general it is not 

 until after the fourth or fifth moulting that these animals become fitted for repro- 

 duction. J 



Those species which have pulmonary sacs§, a heart with very distinct vessels, 

 and six or eight eyes, compose the first Order, Arachnida pulmonaria. 



The others respire by tracheae, and do not possess organs of circulation ; or, if 

 they be present, the circulation is not complete. The tracheae are divided near their 

 origin into ditFerent ramifications, and do not form, as in the Insects, two canals, 

 running parallel with the entire length of the body, and receiving the air in its 

 diiFerent parts by numerous breathing pores. Here we can only distinctly perceive 

 two 11 at most, situated near the base of the abdomen. The number of the simple 

 eyes is four at the most. These form our second and last Order, Arachnida 

 trachearia. 



• These or^aus do not differ from true legs, except in their tarsi, 

 composed of a single joint, and generally terminated by a small hool^, 

 similar to the ordinary legs of the Crustacea. These maxillae and 

 palpi appear to correspond with the palpigerous mandibles of the 

 decapod Crabs, and to the two fore-legs of Limulus ; the four follow- 

 ing legs of Phalangium have a basal maxillary appendage, analogous 

 to the four maxilla of the preceding animals, described by me iu my 

 monograph of the French Phalangia, years before Savigny's Memoirs 

 were published. Hence it is easy to refer all these articulated 

 animals to one general type, and hence the Arachnida are not a kind 

 of Crustaceous animals, destitute of a head, as Savigny says. 



t M. Strauss and myself have only observed one orifice, although 

 Bavigny admits (but, as it seems to me, incorrectly) two. 



t We have also seen that the Argulus does not attain this power 

 nulil after the sixth moult. The same fact is also applicable to 



Lepidopterous insects, and probably to others which change their 

 skins several times — thus. Caterpillars moult four times before 

 assuming the chrysalis state, which is eflfected by a fifth muult, and 

 the insect does not become an imago until after another, which makes 

 six moultings. 



j Sacs inclosing aerial branchix, or performing the office of lungs, 

 and which I distinguish from the latter organs by the name of pneumo- 

 branchiae. 



1 The Pycnogonides are destitute of spiracles, and thus appear to 

 approach the terminal Crustacea, such as Dichelestium and other 

 Entomostraca suctoria. Savigny considers them most allied to the 

 LcEmodipodous Crustacea, from which, however, they widely differ iu 

 me structure of the mouth, eyes, and legs. We believe them to be- 

 long rather to the clais Arachnida, near to Phalangium, consideruiK 

 they may respire by the surface of their skin. 



