ACAULON. 



[ 6 ] 



ACHETA. 



f. 5. Snrcoptes muse, Koch, Crust. iS-c. 

 f asc. 5. pi. 13 ; Ou the mouse, Murray, p. 315. 

 Hypopus. See llvpoi'us. 

 A destructive disease in the sugar-cane is 

 caused in various parts of the world by a 

 minute red Acarus, which swarms round 

 the stem. 



BiBL. Dup-es, Ann. d. Sc. Xaf. 2 ser. ii. 

 p. 40 ; Koch, Deutschl. Crust. ; Walckenaor, 

 Apteres, 3 (Gervais) ; Fiuuouze and Eobin, 

 Journ. d. VAnut. I<s67, oOo, oOl ; Buisduval, 

 L'Untomol. hurticole, p. 76 ; 3Iic. Soc. 

 Jn. l>i80,Gl>/c. dev. p. 249; Murray, ^c.^«^. 

 1880 ; Meo-nin, Parasites, 1880. 



AOAU'LON, C. Midler.— A genus of 

 Phascacete (Acrocarpous Mosses), taken as 

 a section of Phascum by Wilson. A. muti- 

 cam is common on mnist banks. 



BiBL. Mliller, Syno]>s. Mtisc. i. p. 21 ; 

 Wilson, Bryol. Brit p. 20. 



ACEPH'ALOOYSTS.— A term used to 

 denote certain simple sacs filled with a trans- 

 parent liquid, found in the bodies of ani- 

 mals, and usually known as Hydatids by 

 pathologists. They were formerly regarded 

 as distinct parasitic animals ; but recent 

 observations show that they often consist of 

 the cysts or larval forms of cestoid Entozoa. 

 The cysts in many cases contain at first 

 only an amorphous substance or a liquid. 

 At a later period their real nature is deter- 

 mined by the presence of the included 

 Echinococcus — head and hooks. The .sacs 

 or vesicles are oval or spherical, and vary 

 in size from a pin's to a child's head. The 

 walls of the sacs vary in thickness and 

 transparence. They present no appearance 

 of either head or body. In the larger cysts 

 the walls are distinctly laminated. They 

 exhibit no fibrous structure, but appear 

 composed of a homogeneous substance 

 closely resembling albumen in properties. 

 Two species have been distinguished : — 



A. oidof/om (socialis vel jiro/ifcra), the 

 pill-box liydatid of Hunter. This is met 

 with in the liver, kidney, ovary, testis, and 

 caA'ity of the abdomen. When developed 

 in the substance of an organ, it is always 

 enveloped by areolar tissue. The secondary 

 cysts are detached from the inner surface of 

 the parent. 



A. cx(uiena : in this the progeny is de- 

 veloped from the outer surface ; found in 

 the ox and other dometic animals. 



In the examination of cysts supposed to 

 be hydatids, careful search should be made 

 for the hooks of ErhinococcKs or Ci/sticcrcus 

 which can frequently be found when no 



further remains of the body are distinguish- 

 able. The hooks are figured in PI. 21. 

 tig. lb. See E.xtozoa and Echinococ- 

 cus-. 



ACERVULI'NA. Schultze.— Under this 

 name Schultze, in 1854, grouped as a genus 

 some of the adherent varieties of Planorhn- 

 lina variabilis, D'Orb., that have an irregular 

 growth, with heaped chambers. They are 

 found in Avarm .seas, attached to algfe and 

 other bodies. The word " acervnliue " is 

 applied to any such wildly aggregated 

 growth in Foramiuifera. 



BtBL. Schultze, Orf/anism. Polythal. 67 ; 

 Carpenter, P'oram. 200. 



ACETIC ACID.— This is the well- 

 known acid of vinegar. 



It occurs in the juice of the flesh of ani- 

 mals ; sometimes in the stomach in indiges- 

 tion ; also in the human blood after the use 

 of alcoholic liquors, and in that of animals 

 whose food has been soaked in spirit. It is 

 also a common product of the decomposition 

 of vegetable substances, both by fermenta- 

 tion, and in distillation, as well as a com- 

 ponent of the natm-al plants, mostly com- 

 bined with lime or potash ; it is also a rare 

 constituent of some mineral waters. 



The only salt of this acid requiring men- 

 tion is the acetate of copper (neutral), which 

 is made by dissolving common verdigris in 

 excess of dilute acetic acid, filtering and 

 crystallizing upon the slides. The crystals, 

 when mounted -in Canada baUam, exhibit 

 well the phenomena of dichroism. PL 30. 

 fig. 2. 



Acetic acid is one of the most connnon 

 and valuable micro-chemical reagents. It 

 is particularly useful on account of its action 

 upon animal cells in general, rendering the 

 cell-walls transparent aud the nuclei more 

 distinct. The ordinary strong acid (sp. gr. 

 1044) should be used. 



ACETEXOP'SIS, Kent.— A genus of Eu- 

 fusoria, familv Ophrvodendrid;i3. 



BiBL. Kent, Man. Infus. 1880. 



ACIIAPtAD'RIA, Wright.— A genus of 

 Ilydroid Zoophytes. 



A. larynx resembles in habit Tiihularia 

 larynx ; polypes orange. Marine ; on stones. 



i3iBL. Str. Wright, Qu. Mic. Jn. 186-5, 

 iii. p. 50 ; Ilincks, Brit. Zoopln/t. p. 133. 



ACIIE'TA.— A genus of Ort'hopterous in- 

 sects, one species of which, A. domestica, the 

 house-cricket, is familiar to every one. The 

 general structure of this insect agrees so 

 closely with that of Blatta oricntalis, the 

 common cockroach or black beetle, which is 



