ACAREA. 



[ 3 ] 



ACARUS. 



v^Tith hairs of whitish colour, appressed and 

 closely adherent in the diy state, being ap- 

 parently glued together at their extremities. 

 When placed in water the haus are set free 

 and spread out on all sides; they are then 

 seen to consist of clusters of from five to 

 twent}^ spiral cells firmly coherent below, but 

 free above and separating from the cluster 

 at different heights, expanding in all chrec- 

 tions like plumes, and forming a very beau- 

 tiful microscopic object. The free portions 

 of the cells elongate so as to separate the 

 coils of one, two, or occasionally three in- 

 ternal spu'al fibres, which are sometimes 

 branched and not unfrequently broken up 

 into rings ; at the lower part of the cells the 

 turns of the spiral are connected by perpen- 

 dicular processes so as to convert the spiral 

 into a reticulated structm-e. See Spiral 

 STRUCTURES of plants. 



BiBL. Linnean Transactions, xis. 65. 



ACAREA. — A family of Arachnidous ani- 

 mals belonging to the (3rd) Order, Acarina 

 (see Arachnida). 



ACARINA. — An order of Arachnida. 



ACARUS {Tyroglyphus). — A genus of 

 Arachnidous animals, belonging to the order 

 Acarina and family Acarea. 



Char. The body presents a transverse fui'- 

 row between the 2nd and 3rd pairs of legs ; 

 legs nearly equal, entire, and terminated by 

 an acetabulum. 



These animals are commonly called mites, 

 and every* one is familiar with them as occur- 

 ring in cheese, sugar, and flour, &c. The 

 parts of the mouth, and basal joints of the 

 legs, &c. of the Acari can be best made out by 

 crushing the animals upon a shde with a thin 

 glass cover ; then washing away the exuding 

 substance with water, as directed in the 

 Article Preparation; sometimes hot so- 

 lution of potash is requisite, with the subse- 

 quent addition of acetic acid and fiuther 

 washing. When subsequently diied, and 

 then immersed in Canada balsam, the vari- 

 ous parts become beautifidly distinct and 

 may be permanently preserved. 



1. Ac. domesticus (PI. 2. fig. 1), the 

 common Cheese-mite. Body oval, soft, 

 whitish, turgid and fiunished with long fea- 

 thery hairs (b). The transverse fui-row^ (c) 

 occurs at about the anterior fourth of the 

 body, and another is seen between the head 

 and the part corresponding to the thorax. 

 The head is susceptible of elevation and de- 

 pression. In its natm-al state it appears 

 conical {d), and is furnished with two large 

 mandibles ; these consist of a soft retractile 



basal joint (e), and a second dilated, non-re- 

 tractile joint (/) resembling the fixed claw 

 of a lobster, and a moveable piece (/) work- 

 ing against the latter. The two last pieces 

 are toothed where in contact with each other. 

 These mandibles can be advanced separately 

 or together, and be separated or approxi- 

 mated. When in a state of repose, they form 

 as it were a roof above the labium. The 

 labium (^r) is quadi'ilateral, elongated, notched 

 at the end, thin anteiiorly and in the middle, 

 and consolidated laterally with the palpi, 

 which are 4 or 5-jointed (hh). The legs are 

 reddish, inserted in two separate groups, but 

 not very far distant as in Sar copies. The 

 anterior pair of legs are remarkable for their 

 size in the male, which is smaller and more 

 active than the female ; the third pair are the 

 shortest and smallest; the third joint or 

 femur is larger and longer than those next it ; 

 the sixth joint is long and thin ; the seventh 

 joint is furnished with a cordiform membra- 

 nous caruncle, and a single simple claw or 

 hook ; rostrum and legs reddish. 



This species is viviparous and oviparous, 

 and the eggs very numerous. 



These mites are very abundant upon old 

 cheese, the powder of which entirely consists 

 of them, with then' eggs and excrement. 



2. Ac. longior. Body oblongo-ovate. 

 Found upon Gruj-ere and Dutch cheese (PI. 

 2. fig. 2). 



3. Ac. bicaudatus. Abdomen fm-nished 

 with two pediform tubercles, beneath the 

 base of each of which is a stigma. Found 

 upon the feathers of an ostrich. 



4. Ac. farincB. Found in bad flour. 

 DeGeer, Mem. vii. p. 97. pi. 15. fig. 15. 



5. Ac. destructor. Somewhat resembles 

 Ac. domesticus, but said to differ in not having 

 the rostrum and the reddish legs, and in 

 ha\ing long black hau's. It feeds upon the 

 contents of entomological cabinets, especially 

 butterflies. Schrank, Enum. Ins. AustricB, 

 sp. 1057; Lvonet, Mem. Mus. xviii. p. 284. 

 pi. 12. fig. 10-12. 



There is another Acarus which well de- 

 serves the name of destructor, from its de- 

 structive effects upon di'ied insects ; it differs 

 from the Ac. domesticus only in having a more 

 strongly marked fm-row, in the legs being 

 shorter, and the two foremost pau-s being 

 somewhat more widely separated at their 

 origin ; the sixth joint is particularly short. 



6. Ac. lactis. Found upon preserved 

 cream. Fabricius, Spec. Ins., ii. 490. 



7. Ac. Dysenteric. Nyander, Amcenit. 

 Acad. V. p. 97 ; Linn. Gmel. p. 2929. Found 



b2 



