ARACIINIDA. 



451 



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

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

 the mandibles, and called tlie sternal tongue by Savigny in Phalang'mm copticmn, 

 and whicli is composed of a beak-hke prominence, produced by the union of a very 

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

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

 called the mandibles, generally constitute, with certain modiiications, the mcjuth of the 

 majority of the Arachnida. The pharyiiKf is placed in front of a stei'nal prominence, 

 which has been considered as a lip, 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 bj' an additionod one, and all arc annexed to the tliorax (or rather 

 cephalothorax), 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 Scoi-pions, which, in consequence of 

 tlieir 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 alive, or upon 

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

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

 are found only in flour, cheese, and upon various \'egetables. 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.! 



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

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



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

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

 origin into ditterent 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 

 dift'erent parts by numerous breathing pores. Here we can only distinctly perceive 

 two II 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 

 (rachearia. 



• These orgiaris do not differ from true legs, except in their tnrsi, 

 cijo^pose'J of M single joint, MiiU jjener-tliy termiiiiiteO \)y a sriiiill hook, 

 siniiliLr to tlie ordinary legs td the Crustaueii. These mnxillte and 

 |,,il|,i aiJiieiir to eorrespoiid witli the palpitjeroos nuitidibles of the 

 dtcapod Cr:ibs, ajid to ilie two fi.re-le(,'8 of Linuilus ; the four follow- 

 iiii; lei,-s of riialaii),Huiii have a basal maxillary appendaire, analo(fous 

 In the f.'ur niavilUe of the precediijfj animals, described by me in my 

 riiouoj;raph of the Freneli Phalani-ia, years before Savi^jny's liiemoirs 

 were publislied. Henee it is easy to refer all these articulated 

 anlioals to one general type, and licnee the Arachiuda are not a hind 

 of Crustaccous animals, dcstitote of a bead, as Savi),'ny says. 



t HI. Strauss and myself have only observed one orifice, althougli 

 Savitrny admits {bat, as it seems to me, incorrectly) two. 



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



111 after 



Tlie 



:nc fact 



also a|.p 



■able to 



Lepidopterous insects, and probably to others which change their 

 skias several times — thus. Caterpillars moult four times before 

 assuming the chrysalis state, which is effected by a fifth raoalt, and 

 the insect does not become an imago until alter another, wliieli makes 

 six monltings. 



ij Sacs inclosing aerial brmiehiLe. or performing the office of lungs, 

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

 branchite. 



U The Pyenogonides .are destitute of spiracles, anil thus appear to 

 approach the terminal Crustacea, such as Diehelesilum and other 

 Entomostraea suctoria. Savigny considers them most allied to the 

 Ltcniodipndous Crustacea, from which, however, tiiey widely differ in 

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

 long rather tti the class Arachnida, near to phalangium, eoiisidenng 

 they may respire by the surface of their skin. 



G G 2 



