788 



ECHINUS KCFIO. 



InncUudinal furrow, bordered on ench side by movable spine-, 

 and oritires for the tubular or retractile feet ; mouth central 

 and pl.iccit beneath, at t'le union of tin- furrows. 



'I'lii- animals MI this genus arc known by the name "f star. fish, 

 and are common on most coasts. They feed on marine worm-, 

 and the smaller Crustacea. 



SECTION IV. CRINOID.S. 



The animals uf this .M-I lion have been divided into four sub- 

 sections by Mr Millar. 



1. Plates of the body or pelvis resting on the last columnar 

 joint, am) forming tin- cup containing the viscera, articulated 

 with each other by lip-Uke transverse processes; having a 

 minute perforation. The genera are Apioeriniies, and 



Pentacrinu* Europmu. The pelvis consisting of five plates, 

 supporting five rostils ; column not enlarging at the summit; 

 tinkers formed of a single series of joints ; column pentagonal ; 

 the articulating MM luce of the columnar joints petal. shaped. 



This animal has been found alive at the cove of Co/k 



3. 1'l.it. -s of the body articulating imperfectly with each 

 other by transverse processes having a minute central perfora- 

 tion. Hut one germs, PoterioerlnitM. 



:<. Having the plates of the body adhering by sutures 

 lined by a muscular ligament. The genera are Legothocrinites, 

 Actinocrinites, Khodocrinite.s, and Platyrriuites. 



4. The plates of the body anchylosing with the last columnar 

 joint. 



These different genera have all been found in a fossil state 

 in the. limestone in different parts of Great Britain, and are 

 known by the names of Lily Kncrinites, St Cuthbert's beads, 

 he. See Organic Remains. 



DIVISION II. ACALEPHA. 



Animals with a gelatinous body, circular, and radiated in 

 their structure, with a soft, transparent skin, susceptible of 

 contraction and dilatation. 



Cuvier formed a distinct class of this division, under the de- 

 signation of Acaleplm. It comprehends the Radiairet Medu- 

 .'//>. and Anomnlea of Lamarck, together with the genus 

 Actinia, which he embraced in his class Echinodermiitn. 



The Acalepha are either fixed by a base, or float at free- 

 dom in the ocean, suspended by the air which is contained in 

 their bodies, or by being themselves of less specific gravity than 

 the surrounding fluid. Their bodies are not fibrous, but con- 

 sist of a gelatinus substance, which is susceptible of dilatation 

 and contraction. The vessels found in some of these animals, 

 con-ist merely of canals unprotected by any coating, which 

 are connected with the stomach, and penetrate the gelatinous 

 mass in various directions. There is no cavity for the recep- 

 tion of intestines ; they do not appear to have any muscular 

 action. On their inferior surface in the centre they are provided 

 with a mouth, or suckers, or tentacula, none of which, how- 

 ever, are furnished with hard parts. The stomach, or organ 

 of digestion, consists of a simple sac, unprovided with any out 

 let ; between which and the external skin is a simple, but 

 obscure organization. The external surface of many of the 

 species displays a fine arrangement of beautiful colours. They 

 are common to the seas of ail countries, and emit a phosphor, 

 esceut light in the dark. 



SECTION I. BODY FIXED. 



Although these animals are usually fixed by their base to 

 rocks, stones, &c., yet they have the power of moving on their 

 h.i-c. from one situation to another, or of detaching themselves 

 entirely, and swimming at freedom in the ocean. 



The genera of the section are Zoanthus, Lucernaria, and 



Actinia Verrucosa, pl.32 f. 11. With a cylindrical, fleshy, sim- 

 ple and very contractile body, fixed by its base, but having 

 the power of removing itself; mouth terminal, and having 

 one or many rows of radiated tentacula, which they can con- 

 tract entirely. They have the appearance of a flower in blos- 

 som ; hence their familiar name, sea anemone. 



They feed on the smaller marine animals, ejecting the undi- 

 gested parts by their mouths. 



SECTION II. BODY FREE. 



The general fieure of these animals is a disk, of various de- 

 grees of convexity above, and not unlike the head of a mush- 

 room ; and having the mouth below, which is somewhat leng- 

 thened into a pedicle, and furnished with variously formed 

 tentacula. 



The genera are Phorcynia, Pelagia, Cyanaea, Rhizostoma, 

 Oassiopea, Geryonia, Or'ythia, Berenix, Eudora, Carybdea, 

 Beroe, Cestum Diphytes, Porpita, Venella, Physalia, Physso- 

 phora, Ulnzophyza, and Stephanomia. 



ECHINUS, or SEA EGG ; a marine animal, in- 

 habiting the seas of most countries, and subject to 

 great variety in the species. Echinus esculentus, 

 the edible sea egg, is common on the coast of Europe, 

 and is esteemed as an article of food. In systematic 

 arrangements, the genus echinus of Linnaeus has been 

 much divided, and is at present restricted to those 

 species which have an orbicular, oval, or globular 

 body, covered with spines, articulated on imper- 

 forate tubercles. These spines are very slightly 

 attached, and fall off the dead animal on the least 

 friction ; in consequence, the specimens which com- 



monly come under observation are deprived of 

 them entirely. Five ranges of pores diverge from 

 the summit, and tend to the centre beneath, di- 

 viding the shell into well marked sections. The 

 mouth is situated on the inferior surface, in the cen- 

 tre, and is armed with five osseous pieces or plates ; 

 anus superior. Many species are ornamented with 

 a profusion of long and pointed spines, while, in 

 others, they are quite short. It is by means of these 

 spines tliat the animals change their position. ;md 

 move from place to place. The apparatus of the 

 month is provided with strong muscles, and is well 

 calculated for crushing the hard portions of the ani- 

 mal's food. In the same species the colours vary 

 considerably, the traits changing, however, on the 

 deatli of the animal. Echini are said to retreat to 

 deep water on the approach of a storm, and preserve 

 themselves from injury by attaching themselves to 

 submarine bodies. E. melo is perhaps the largest 

 species known, and is found not uncommonly in the 

 Mediterranean. Many fine species have been dis- 

 covered in a fossil state, imbedded in chalk, &c., in 

 beautiful preservation. See Espinodormata, Section 

 II. Echinides. 



ECHO ; daughter of the Air and Tellus ; a nymph, 

 who, according to fable, was changed by Juno into 

 a rock, because her loquacity prevented Juno from 

 listening to the conversation of Jupiter with the 

 nymphs. The use of her voice, however, was hsft her 

 so far as to be able to repeat the last word which she 

 heard from others. Another account is, that Echo 

 fell in love with Narcissus, and, because he did not 

 reciprocate her affection, she pined away, until no- 

 thing was left but her voice. 



ECHO. When sound strikes against a distant hard 

 surface, it is reflected, and heard again after a short 

 space ; this repetition is called echo. If the sound 

 is repeated several times, which is the case when it 

 strikes against objects at different distances, many 

 echoes are heard. This phenomenon -is not caused 

 by a mere repulsion of the sonorous particles of air, 

 for then every hard substance would produce an 

 echo ; but it probably requires a degree of concavity 

 in the repelling body, which collects several diverg- 

 ing lines of sound, and concentrates them in the place 

 where the echo is audible, or, at least, reflects them 

 in parallel lines, without weakening the sound, as a 

 concave mirror collects in a focus the diverging rays 

 of light, or sometimes sends them back parallel. 

 Still, however, the theory of the repulsion of sound 

 is not distinctly settled, probably because the nature 

 of reflecting surfaces is not sufficiently known. The 

 reflecting surface must be at a certain distance, in 

 order that the echo may come to the ear after the 

 sound, and be distinctly separated from it. Obser- 

 vation proves that sound travels 1 142 feet in a second ; 

 consequently, an observer, standing at half that dis- 

 tance from the reflecting object, would hear the echo 

 a second later tlian the sound. Such an echo, then, 

 would repeat as many words and syllables as could 

 be heard in a second. This is called a polysyllabic 

 echo. If the distance is less, the echo repeats fewer 

 syllables ; if only one is repeated, then the echo is 

 monosyllabic. The most practised ear cannot dis- 

 tinguish, in a second, more tlian from nine to twelve 

 successive syllables, and, for a monosyllabic echo, a 

 period of at least half a second is requisite. Hence 

 we see why arched walks and halls echo, without 

 producing a clear and distinct sound. Some of the 

 walls are too near ; and some form an uninterrupted 

 series of surfaces at different distances, and the ear 

 is not able to distinguish the original sound from the 

 first echo, nor to separate the nmnerous echoes which 

 are thus confounded with each other. On the con- 

 trary, if several reflecting surfaces are at different 



