470 
ARACHNIDA. 
terminated in various ways, according to their habits. Some of these insects {Acarides, Latr.) have 
eight legs, fit only for walking, and chelicerse. 
Tromb'tdium, Fabr., has the chelicerse terminated by a moveable claw; palpi projecting, pointed at tip, with a 
moveable appendage or finger beneath the extremity; two eyes, each at the top of a small fixed peduncle. T. holo- 
sericenm, Fabr., very common in gardens during spring, of a blood-red colour, with the abdomen nearly 
square, and narrowed behind. A much larger species (T. cinctarhm, Fabr.) inhabits the East Indies, and emits a 
red dye. 
Er})thr<sus, Latr., has the chelicerae and palpi of Trombidium, but the eyes are sessile, and the body not divided. 
E. phalangioicles, Latr. 
Gamamis, Latr., has the chelicerae didactyle, and the palpi projecting, distinct, and filiform. In some, the body 
is covered entirely, or in part, by a scaly skin, but in others it is entirely soft. Some of the latter species live upon 
different birds and quadrupeds. Others, as the Acarus telarius, Linn, [or the Red Spider of the hot-houses], form, 
upon the leaves of various vegetables, especially upon those of lime-trees, very fine webs, which injure them greatly. 
This species is reddish, with a black spot on each side of the abdomen. 
Cheyletus, Latr., has didactyle chelicerae ; but the palpi are thick, arm-like, and terminated by a sickle-shaped 
joint. A. eruditiis, Schr. 
Oribafa, Latr. (Notaspis, Herm.), has the chelicerae also didactyle ; the palpi very short, or concealed; the body 
covered with a hairy, scaly skin ; feet long, or moderate. The front of the body is advanced like a beak. Found 
upon stones, trees, in moss, &c. They creep but slowly. 
Uropoda, Latr., has, from analogy, forceps-like chelicerae ; palpi not projecting ; body covered with a scaly .skin; 
legs short ; anus with a long thread, by which this insect is attached to various beetles, and suspended in the air. 
A. vegetans, De Geer. 
Acarus, Fabr. (Sarcoptes, Latr.), has two didactyle chelicerae ; palpi very short, or con- 
cealed ; body very soft ; tarsi terminated by a vesicle. Some species feed upon our ali- 
mentary substances (A. domesticus, A. fariitce) ; others are found in the ulcers of the itch 
in man, the horse, cat, dog, &c. {A. scab'iei. See the Thesis of Dr. Galet upon this species). 
Fig. 3i). — Acarus douiesticus 
niagiiilied 
Fig 40.— Ixodes 
piumbcus, and 
its beak, mag- 
nified. 
Other Mites or Ticks (RicixiiE, Latr.) have also eight legs, formed for walking, 
but destitute of chelicerae, which are replaced by lancets, forming, with the tongue, 
a sucker. Some have the eyes distinct. 
Bdella, Latr., having the sucker advanced and beak-like, with long, elbowed palpi, and four eyes. Scirus longi- 
rosfris, Herm. 
Smaridia, Latr., with palpi short and straight, and two eyes. A. sambuci, Schr., &c. 
The other Riciniae have not the eyes perceptible ; the palpi are in the shape of valves, dilated at the 
ti]), serving as a sheath to the sucker, of which the parts are horny and toothed ; the body is clothed 
with a corneous skin, or at least with a scaly plate in front. These ticks are parasites, sucking the 
lilood of various vertebrated animals ; and although at first very much flattened, they acquire, by suc- 
tion, a very large size, and become swollen out like a bladder. They are round or oval. 
Lrodes, Latr. {Cynorluestes, Herm.), has the palpi casing the sucker, and forming, with it, a pro- 
jecting beak, truncated, and slightly dilated at the tip. They are found in thick woods, abounding 
in brush-wood, briers, &c., attaching themselves to low plants by the two fore-legs, extending the 
other feet. They fasten upon dogs, cows, horses, and other quadrupeds, and even upon the tortoise, 
burying their suckers so completely in their flesh that they can hardly be detached by force, and by 
tearing away the portion of skin to which they are fastened. They deposit a prodigious number of 
eggs, discharging them from the mouth, according to M. Chabrier.* Their multiplication upon the 
ox and horse is sometimes so great that these animals perish from exhaustion. The tarsi are termi- 
nated by two ungues inserted upon a plate, or are united at the base upon a common peduncle. The 
ancients appear to have known these animals under the name of Ricini. They are our well-known 
Ticks, — Ixodes ricinus, Linn., attacking the Dog; and Ix. reticulatus, Latr., Fabr. {Acarus reduvius, 
Schr.), the Ox. The latter, w'hen swollen, is half an inch long. The study of the species of this genus 
is not sufficiently advanced. 
Argas, Latr. {Rhgnchoprion, Herm.), differs from Ixodes in the inferior situation of the mouth, and the palpi 
not encasing the sucker, and being 4-jointed instead of three. A. reflexus, Fabr., Latr. Upon pigeons. A. persicus 
(Malleh de Mianeh), described by travellers under the name of the Venomous Bug of Miaha, has been the subject 
of a curious memoir by M. Fischer de Walldheim. [This insect formed the subject of much discussion at the 
Liverpool meeting of the British Association] . 
[M. Audouin has described and figured some species of the two preceding genera, and of those of Tetranychus 
and Pteroptus, in the Annales des Sci. Nat. for 1832.] 
Other Mites {Hydraehnellce, Latr.) have also eight legs, but they are ciliated, and fitted for swimming. 
They form the genus Hydrachna of Muller {Atax, Fabr.), and live only in the water. The body is oval 
* [The anal orifice being; minute, and close to the mouth, has been mistaken for tlie latter in this observation.] 
