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are most commonly met with in our climate 

 when examined in their native element, are 

 seen to be composed of a large mushroom- 

 shaped gelatinous disc, from the lower surface 

 of which various processes and filaments 

 depend. There are, in fact, obvious points 

 of resemblance among them all ; but still 

 they admit of division into genera and sub- 

 genera. Thus, we may observe, the genus 

 Medusa includes those which have a central 

 disc, more or less convex, on the upper sur- 

 face, something like the head of a mush- 

 room, and those that have a true mouth on 

 the under-side of the disc ; but this mouth 

 is sometimes a simple opening, and at other 

 times placed on a peduncle : while the genus 

 jEqu&rea includes those in which the mouth 

 is simple, and not on a peduncle. When 

 the disc is furnished with tentacula all 

 round, they are the ^quorea strictly so 

 called, and one of the most numerous among 

 the Acalephae in the seas of warm climates. 

 There are many others ; and it would ap- 

 pear that their tentacula possess consider- 

 able muscular power, and that they are 

 capable of drawing towards the mouth many 

 small Molluscous and Crustaeeous animals. 

 [See JELLY-FISH.] 



ACANTHOCEPHALA. A genus of pa- 

 rasitic worms belonging to the Parenchy- 

 mata, an order of the Entozoa. As an ex- 

 ample, the Echinorhyncus yigas, often found 

 in abundance in the alimentary canal of 

 swine, may be named. The form of this 

 parasite is elongated, tapering to the tail : 

 the head consists of a retractile snout or 

 proboscis, armed with four circlets of sharp 

 recurved spines, and it can be withdrawn or 

 protruded at will. At the extremity of this 

 spine-armed proboscis is the mouth, a simple 

 suctorial orifice leading to a double nutritive 

 canal. 



ACANTHOCrNTJS. A genus of Coleop- 

 terous insects belonging to the Longicorn 

 group. There are but few European species : 

 the antennae in the male are more than 

 four times the length of the body. 



ACANTHOPHIS. A genus of venomous 

 serpents, allied to the Vipers, but distin- 

 guished from them in many essential cha- 

 racters. The head of the Acanthophis is broad 

 and compressed, the mouth capable of great 

 extension, and the tail is terminated by a 

 little spur or horny excrescence, whence its 

 name is derived. They are natives of Aus- 

 tralia ; secrete themselves in holes or beneath 

 the roots of trees, and exhibit an astonish- 

 ing tenacity of life. The A. Brownii is 

 reckoned the most venomous Reptile found 

 near Port-Jackson. 



ACANTHOPODA. A tribe of Clavicorn 

 Coleopterous insects (composed of only one 

 genus, ftettrocerus), distinguished by their 

 flattened feet, which are broad, and armed 

 on the outside with spines ; the tarsi short 

 and four-jointed with ordinary sized claws, 

 and the body depressed ; the prosternum is 

 dilated ; the antennae are rather longer than 

 the head, eleven-jointed, the last six forming 

 a nearly cylindrical serrated mass. 



ACANTHOPTERYGII. One of the three 

 primary grand divisions, or natural orders, 

 of fishes ; originally recognized by our coun- 

 trymen Willoughby and Ray, afterwards 

 systematized by Artedi, and since established 

 by Cuvier. The characteristics of the Acan- 

 thopterygii are, that they possess bony skele- 

 tons, with prickly spinous processes in the 

 dorsal fins. The Stickleback and Perch are 

 familiar examples of this division. 



ACANTHURUS, or SURGEON-FISH. A 

 genus of Acanthopterygious fishes, many of 

 which are remarkable for the beauty of their 



SURGEON PISH. (AOANTHUBTJS ) 



form and the variety of their colours. They 

 are chiefly distinguished by the sharp and 

 lancet-like moveable spines with wliich they 

 are armed on each side of the tail ; hence, 

 as they cannot be handled incautiously with 

 impunity, they have obtained from English 

 sailors, &c., the name of " doctors." They 

 abound in the tropical seas, but are never 

 seen elsewhere. 



Of these small spider-like 

 animals, M. Latreille makes four divisions : 

 1. Mites, (Trombidites) ; 2. Ticks, (Ricinitcs) ; 

 3. Water Mites, (Hydrachnellce) ; and 4. 

 Flesh Worms (Microphthira). Some of these 

 exist on the ground, others in the water ; 

 some are parasitical, living on the blood and 

 humours of the animals or insects on which 

 they are fixed, while others insinuate them- 

 selves under the skin, where they multiply 

 prodigiously. Of these latter, the Itch-insect 

 (Sarcoptcs scabici,) is a remarkable example. 

 Their mouths are, in general, formed rather 

 for suction than for mastication ; and their 

 extremities are commonly armed with what 

 may be likened to a small pair of pincers. 

 Some have four eyes, some two, and several 

 appear to have none. The common Cheese- 

 mite (Acarus dmnesticus*) 

 is familiar to every one. 

 Another has the power of 

 spinning webs, and is well 

 known as the Red Spider, 

 in hot-houses, where it 

 greatly injures the plants 

 by covering the leaves with 

 its webs. There are also 

 Ticks, Harvest-bugs, Wa- 

 ter Mites, and many others, 

 which will be noticed in 

 their alphabetical order. 

 We may here, however, 

 observe, en passant, that so widely are the 

 Acaridee disseminated through animate 



