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, andthe young of the Pyc- 
nogonidae have, also, only four. With Phrynus, 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, 
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, different from this type, but the three other pairs have a great 
number of articles, each tarsus having four. But the Phalangidae 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 
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 Gilycipha- 
which, with the Araneae, with Chelifer and Pha- ieee 
gus, but with the anterior legs, only, with Sarcop- 
tes. 
dangium, have been taken by Treviranus (Bau 
d. Arach. p. 23, Taf. II. fig. 17-19, Taf. III. fig. 
28, and Verm. Schrift. I. p. 18, 33, Taf. II.) for the 
stigmata, see Brandt, Mediz. Zool. loc. cit. p. 88, 
Taf. XV. fig. 8, c. c., and Ann. d. Sc. Nat. loc. cit., 
and Wasmann, loc. cit. p. 3. fig. 1, 6, 24. 
1See Duges, Ann. d. Sc. Nat. I. p. 7, and 
Erichson, Entomogr. Heft. I. p. 7. 
2 Most usuaky there are two nails to each foot ; 
but Phalangium, Hoplophora, and Damaeus, 
have only one; while Segestria, Lachesis, and 
The posterior legs of this last genus, and all 
of them with the Tardigrada, and with Demodex 
Jfolliculorum, are only simple stumps. 
5 For example, with Ixodes, Argas, Dermanys- 
sus, Pteroptus, &c. 
6 With Sarcoptes ovis and cati, this arolium is 
absent with the penultimate pair of legs ; and with 
Sarcoptes equi, with the last pair. With Sar- 
coptes cynotis, rupicaprae, and scabiei, it is 
wanting with the last two pairs. With Sarcoptes 
- Clotho, as well as Demodezx, Pelops, Zetes, and 
“Oribates, have three, and Emydium and’ Macro- 
biotus have even four. 
8 Sce the figures of Savigny, loc. cit. 
4 The articulations are few and indistinct with 
Ippop , Glycyphagus prunorum, and Meli- 
chares agilis, all the legs have long pedunculated 
organs of this kind ; see Hering, Die Kritzmilben 
der Thiere, in the Noy. Act. Nat. Cur XVIII. 
part II. Tab. XLIII.-XLY. 
