ACARUS. 



ACEPHALOCYSTS. 



in the dejections of dysentery; also in old 

 casks. 



8. Ac. passerinus. Found upon young 

 birds. DeGeer, vol. vii. 139. Ac. ckelopus, 

 Herm. Mem. Apterol. p. 82. pi. 3. fig. 7. 



9. Ac. passularum. With two very long 

 buccal bristles ; it lives upon dried figs, and 

 other saccharine fruits. Bering, Nova Acta 

 Nat. Curios, xviii. p. 618. pi. 45. f. 14-15. 



10. Acarus plumiger, Koch, Deutschl. 

 Crust., &c. fasc. 5. pi. 15, is said to have 

 feathery hairs ; but this is probably the case 

 in all the Acari, and certainly in many of 

 them (PI. 2. fig. 1 b). Probably in Ac. plu- 

 miger this supposed peculiarity is distinguish- 

 able with a low power, under which these ani- 

 mals have been usually examined. 



Some other species have been formed into 

 new genera, which may find place here. 



a. Glyciphaous (Hering). Body soft, not 

 divided into two parts by a transverse line or 

 furrow ', legs entire, with acetabula. 



11. A. (Gl.) prunorum. Found on dried 

 plums. Hering, Nova Acta Nat. Curios, xviii. 

 p. 619. pi. 45. f. 16-17. 



12. A. (Gl.) hippopodos. Body as broad 

 as long, very acute anteriorly, entirely co- 

 vered with short hairs ; a minute projection 

 at the end of the abdomen. Found upon the 

 crusts of ulcers on horses' feet. Hering, 

 Nov. Act. Nat. Curios, xviii. 607. An unde- 

 scribed Acarus has also been mentioned as 

 occurring upon the feet of sheep affected 

 with the canker. Grognier, Zool. veter.y.233. 



13. A. (Gl.) cursor. Found in the feathers 

 of the owl and in the cavities of the bones 

 of skeletons. The hairs are jointed. Gervais, 

 Ann. Sc. Nat. 2 ser. xv. p. 18. pi. 2. f. 5 a. 



14. A. (Gl.) (Sarcoptes)palumbinus. On 

 the pigeon. Koch, 1. c. fasc. 5. pi. 12. 



Some other species have been insufficiently 

 examined. 



15. Ac. avicularum, DeGeer, Mem. vii. 

 106. pi. 6. fig. 9. Louse of the grouse. 

 Lyonet, Mem. Mus. xviii. 281. pi. 15. f. J6. 



16. Ac. marilce, Gervais, Diet. Sc. Nat. 

 Suppl. i. 45. 



17- Ac.favorum. Found in old honey- 

 combs. Herm. Mem. Apterol. p. 86. 



18. Ac. fungi, Herm. I. c. 



b. Myobia (Heyden). Body elongate, 

 many-lobed; legs entire, the posterior ones 

 largest. The type of this genus is 



19. A. pediculus musculinus, Schranck, 

 p. 501. pi. 1. f. 5. Sarcoptes musculinus, 

 Koch, Deutsch. Crust, fyc. fasc. 5. pi. 13. 



c. Hypopus. See HYPOPUS. 



BIBL. Duges, Ann. d. Sc. Nat. 2 ser. ii. 



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

 Apteres, 3. 



ACAULON, C.Miiller. A genus of Phas- 

 caceae (Acrocarpous Mosses), including cer- 

 tain species of Phascum of Schreber, &c. 



1. A. muticum, C. Mull.=Phascum mu- 

 ticum, Schreb. 



2. A. triquetrum, C. Mull.=P^. trique- 

 trum, Spruce. 



ACEPHALOCYSTS. A term used to 

 denote certain simple sacs filled with a trans- 

 parent liquid, found in the bodies of animals, 

 and usually known as Hydatids by patholo- 

 gists. They were formerly regarded as para- 

 sitic animals, or entozoa, but recent observa- 

 tions have tended to show that they consist of 

 the cysts of Echinococci, from which the ani- 

 mals have disappeared by death and dissolu- 

 tion, or in which the entozoa have not been 

 formed, or in which they have been overlooked. 

 The cysts in which many hydatids are deve- 

 loped, contain at first only an amorphous sub- 

 stance or a liquid. At a later period their real 

 nature is determined by the presence of the 

 included entozoa. But it appears that in 

 some of them the entozoa are never formed. 

 The sacs or vesicles are described as oval or 

 somewhat spherical; developing smaller 

 cysts between the laminae of the parent, 

 which are discharged from its inner or outer 

 surface. They vary in size from a pin's to 

 a child's head. The walls of the sacs vary 

 in thickness and transparence. They pre- 

 sent no appearance of either head or body. 

 In the larger cysts the walls are distinctly 

 laminated. They exhibit no fibrous struc- 

 ture, but appear composed of a homogeneous 

 substance closely resembling albumen in 

 properties. Regarding these bodies as ani- 

 mals, two species have been distinguished : 



A . endogena (socialisvel prolifera], the pill- 

 box hydatid of Hunter. This is met with 

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

 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 pa- 

 rent. 



A. exogena : in this, the progeny is deve- 

 loped from the outer surface. It is said to 

 be found in the ox and other domestic 

 animals. 



The cysts found attached to the choroid 

 plexus of the human brain, have been denied 

 to be hydatids by pathologists, and con- 

 sidered merely to arise from accidental dis- 

 tension of the coats of the veins. Dr. Bel- 

 lingham however has found that they develop 



