( 



370 TUE 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 umx- 

 illao/" 



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

 nogouidac have, also, only four. With Phrynus, and Thelyphonus, the first 

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

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

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

 the form of feet, and their extremity is not only unguiculuted, 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, 

 stiff Femur ; then a Tibia, divided by an articulation into two unequal 

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

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

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

 number of articles, each tarsus having four. But the Phalangidae diff'er 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 ^Bi 



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 Tyroi^lyphus and Glycipha- 



which, with the Araneae, with CheUfer and Pka- gus, but with the anterior legs, only, with Sarcop- 



lanffium,ha,ve been taken by Treviranus (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 



2S, and Verm. Schrift. I. p. 18, 33, Taf. II.) for the folliculorum, are only simple stumps, 



stigmatii, see Brandt, Mediz. Zool. loc. cit. p. 88, 5 For example, with Ixodes, Argas, Dermanys- 



Taf. XV. fig. 8, c. c, and Ann. d. Sc. Nat. loc. cit., su.i, Pteroptus, kc. 



and iVasmann, Vx. cit. p. 3. fig. 1, 6, 24. « With Sarcoptes ovis and cati, this arolium is 



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



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



1' Most usuaSy there are two nails to each- foot ; coptes cynotis, rupicaprae, and scabiei, it Is 



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- 



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



Oribates, have three, and Emydium and Macro- organs of this kind ; see Hering, Die Kriitzmiiben 



biotus have even four. der Thiere, in the Nov. Act. Nat. Cur. XVIII. 



3 See the figures of Sawg-ny, loc. cit. part II. Tab. XLIIl.-XLV. 



-1 The articulatioua are few and indistinct with 



