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. 



Trombidhim, Fabr., has the chelicerae 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- 

 sericetim, 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. cinciorhtm, Fabr.) inhabits the East Indies, and emits a 

 red dye. 



Ei\i/t/iriei(s, Latr., has the cheliceree and palpi of Trombidium, but the eyes are sessile, and the body not divided. 

 E. plialaiipioides, Latr. 



Gamasus, Latr., has the chelicera; 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 Acanis /elariiis, 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. 



Cheyletiis, Latr., has didactyle chelicera; ; but the palpi are thick, arm-like, and terminated by a sickle-shaped 

 joint. A. eriiditus, Schr. 



Oribata, Latr. {Nutaspis, Herai.), 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. 



Ui-opoda, Latr., has, from analogy, forceps-like chelicera; ; 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. {Sarcoples, Latr.), has two didactyle chelicerie ; 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. farina) ; 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). 



Other Mites or Ticks (Ricixi.e, Latr.) have also eight legs, formed for walking, 

 but destitute of chelicerae, which are replaced by lancets, forming, with the tongue, 



Fig-. 39.— Acarus diiinesticus, ' f J ' O' O > 



magiiiiicd 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- 

 rostris, Herm. 

 iimaridia, Latr., with palpi short and straight, and two eyes. A. sambnci, Schr., &c. 



The other Riciniae have not the eyes perceptible ; the palpi are in the shape of valves, dilated at the 

 tip, 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 

 blood 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. 



Ixodes, Latr. (Cynorhccstes, 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. reticidatus, Latr., Fabr. (Acarus reditvius, 'piumbTuf.'and 

 Schr.), the Ox. The latter, w hen swollen, is half an incli long. The study of the species of this genus Iff^''^^'*' "'"'■'' 

 is not sufficiently advanced. 



Argas, Latr. (Rhynchoprion, 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. rejlexiis, Fabr., Latr. Upon pigeons. A. persicns 

 (Malleh de Mianeh), described by travellers under the name of the Venomous Hug of Jliana, has been the subject 

 cif 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 Annates des Set. Nat. for 1832.] 



Other Mites {Hydrachnellce, Latr.) have also eight legs, but they are ciliated, and fitted for swimming. 

 They form the genus Hydrachna of Miiller {Atax, Fabr.), and live only in the water. The body is oval 



• [The aiiul orifice being raiuute, and close to tiie mouth, has been mistaken for tlie latter in tliis observation.] 



