870 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- 

 noo-onidae have, also, only four. With Phrynus, and Thehjphonus, 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, 

 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 antenuiform pair of feet already 

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

 number of articles, each tarsus having four. But the Plialangidae differ 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 

 iust 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 {Arolitim), 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 acjuatic Hydrachnea, the swin)ming 

 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 Glycipha- 



which, with the Araneae, with Chelifer and Pka- gas, but with the anterior legs, only, with Sarcop- 



langium, have 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 Uiem with the Tardigrada, and with Vemodex 



2S, and Verm. Sclirift. 1. p. 18, 33, Taf. II.) for the fol/iculoriun, are only simple stumps. 



Btigmata, see lirandt, Mediz. Zool. loc. cil. p. 88, a i'or a\iimp\e, -wit)^ Ixodes, Jrf;as,Dermanys- 



Taf. XV. tig. 8, c. c, and Ann. d. Sc. Nat. loc. cit., su.i, Pteroptii.t, &c. 



and H'asmann, loc. cit. p. 3. tig. 1, 6, 24. « With Sarcoptex ovi.i and cati, this arolium is 



1 See Dugix, Ann. d. Sc. Nat. I. p. 7, and absent with the penultimate pair of legs ; and with 



Erichson, Kntomogr. lieft. I. p. 7. Sarcn/ites e(/iii, with the last pair. With Sar- 



;i Most usuafty there are two nails to each foot ; copies ci/nnti», rupicaprae, and scabiei, it is 



Ijut Phalangium, Hoplophora, and Damaeu.i, wanting with the last two i)airs. With Sarcoptes 



liave only one ; while Se.ge.itria, LachexiH, and hippopodrx, (l/i/ry/ilmgus prunoruni, and 3If/i- 



•Clotho, a» well as Deinodex, Felopn, Zetes, and chares agi/is, all tlie legs have long iHilunculated 



Oribates, have three, and Emydium and Macro- organs of thi.s kind ; see Hering, Die Kr ,tzniillHU 



biotus have even four. dor Thiere, in the Nov. Act. Nat. Cur XVIIl. 



a See the figures of Saiiigny, loc. cit. part II. Tab. XLIII.-XLV. 



i The articulations are few and indistinct with 



