370 THE ARACHNOIDAE. § 299. 



line, a tendinous ligament, on which are inserted several of these muscular 

 bands. *^^ It is very probable that these animals can, by this apparatus, 

 compress their abdomen in various directions. 



§ 299. 



The locomotive organs of the Arachnoidae are situated exclusively on the 

 cephalothorax. They consist of only four pairs of legs, of which the first 

 may, perhaps, be regarded as the posterior pair of metamorphosed max- 

 illae.*" 



Some Mites, only, when young, have six feet, and the young of the Pyc- 

 nogonidae have, also, only four. With Phry?ius, and Thelyphonus, the first 

 pair considerably resembles two multi-articulated tactile organs ; but with 

 Galeodes, these same organs have wholly the appearance of legs, excepting 

 they are without claws. With Mygale, the maxillae of the first pair have 

 the form of feet, and their extremity is not only unguiculated, but also pro- 

 vided with a tarsus. The other Arachnoidae have usually nails on all their 

 feet, and, with some, each foot may have four nails.'-' With many Ara- 

 neae, the nails have, on their convex side, a pectinated appendage.*'^* 



As to the types of the articulations of the legs, they are usually as fol- 

 lows ; first, a movable Coxa; then a short Trochanter; then a longer, 

 stifi" Feimir ; then a Tibia, divided by an articulation into two unequal 

 parts ; and, finally, a Tarsus, composed of a long und a short article. With 

 the Phrynidae, not only are the first and antenniform pair of feet already 

 mentioned, difierent from this type, but the three other pairs have a great 

 number of articles, each tarsus having four. But the Phalangidae diifer the 

 most, — the tarsi of all the feet having an extraordinary number of articles. 

 On the other hand, among the lower Arachnoidae, and especially with the 

 Acarina and Tardigrada, there are species with which the seven articles 

 just mentioned cannot be easily distinguished, for the articulations are less 

 in number, or wholly indistinct. With many of these species, some of the 

 pairs of legs, or even all, are reduced to real foot-stumps.*'*' Numerous par- 

 asitic Acarina have, between the nails, a small organ [Arolium), by which, 

 as with a sucker, they can attach themselves to foreign bodies.*^' These 

 organs are most developed with Sarcoptes and allied genera, which are 

 without nails, for they here consist of a long, pedunculated disc upon all, or 

 only upon some of the feet.**" With the aquatic Hydrachnea, the swimming 

 feet have no other peculiarities than that one of their sides is thickly pilose. 



4 For these muscles, the cutaneous insertions of all the eight legs of Tyroglyphus and Olycipha- 



which, with the Araneae, with Chelifer and Pha- gus, but with the anterior legs, only, with Sarcop- 



langium, have been taken by Treviraiius (Bau tes. The posterior legs of this last genus, and all 



d. Arach. p. 23, Taf. II. fig. 17-19, Taf. III. fig. of them with the Tardigrada, and with Demodex 



28, and Verm. Schrift. I. p. 18, 33, Taf. II.) for the foUiculorum, are only simple stumps, 



stigmata, see Brandt, Mediz. Zool. loc. cit. p. 88, S For example, with /a:odes,>4r^as, XJerwianys- 



Taf. XV. fig. 8, c. c, and Ann. d. Sc. Nat. loc. cit., sus, Pteroptus, &c. 



and fVasmann, loc. cit. p., 3. fig. 1, 6, 24. 8 With Sarcoptea ovis and cati, this arohuni ia 



1 See Dugis, Ann. d. Sc. Nat. I. p. 7, and absent with the penultimate pan' of legs ; and with 



Erichson, Entoraogr. Heft. I. p. 7. Sarcoptes equi, with the last pair. With Sar- 



'i Most usua'y there are two nails to each foot ; copies cynotis, rupicaprae, and scabiei, it ia 



but Phalangium, Hoplophora, and Damaeus, wanting with the last two pairs. With Sarcoptes 



have only one ; while Segestria, Lachesis, and hippopodes, Glycyphagus prunorum, and Meli- 



Clotko, as well as Demodex, Pelops, Zetes, and chares agilis, all the legs have long pedunculated 



Oriliates, have three, and Emydium and Macro- organs of this kind ; see Hering, Die Kratzmilben 



biotas have even four. dcr Thiere, in the Nov. Act. Nat. Cur. XVIII. 



3 See the figures of Savigny, loc. cit. part II. Tab. XLIII.-XLV. 



■1 The articulations are few and indistinct with 



