Page:The New International Encyclopædia 1st ed. v. 06.djvu/715

* ECHINODERMATA. 623 ECHTEB. that its mfiiilwis are characteristic index fos- sils of tlio Carboniferous and I'erniian rocks. The class l>ecanie extinct at the close of the Paleo- zoic. The body is inclosed in a bud formed box n:ade up;.;enerally of thirteen plates of regular form and strictly pentaujeral radial arrange- ment. The mouth is at the summit of the calyx, and the anus at the side. There are no arms, and the relatively large ambulacra! areas extend downward over the surface of the calj-.x, some- times nearly to the base or stem. The stem was short or absent. About 20 genera and 150 spe- cies are known. See Pe.ntremites. Tor description of the ontogeny or develop- ment of the echinodcrms, consult the works by Lang and Bather mentioned in the bibliography. The following diagram is intended to represent both tile geological distribution and the phylo- genetic relationships of the various classes: 1 -o E to g i J .3 E ^ i 3 5 1 c 1 1 Q- 1 a: OphiuraifJea Astero'dea — ^ __ ^

,■■ " BUstnidea — 2 ■ ■ J L — — ^^ 51 m ■ — r — — Exhinoidca ■^ — «■ ■ ■ ■ HolothuroideB

^ !T3 "^& rn BlBLiocRAPiiY. For general treatises on both living and fossil forms, see Bather, "The Echi- noderma." in Lankester's Treatise on Zoology, part ii. (London, 1900); this contains a good I'ililiography. Consult, also: Parker and Has- well, Textbook of Zoology, vol. i. (London and Xew York, 1897); Lang and Bernard. Text-Book of Comparatire Anatomy, part ii. (London and Xew York, 1896). also with a bibliogi-aphy. These last two works are technical. Zittel and Eastman, Text-Rook of Paleontology, vol. i. (London and Xew York, 1900), deals almost entirely with the fossil forms. See, also, Alex- ander Agassiz, "Paleontological and Embryo- logical Development," Proeeedings of the Ameri- can Association for the Aelraiicemeiit of Science, Boston Meeting (Cambridge. 1880): Carpenter, "Notes on Echinoderm Morphology," Quarterly Journal of the Microscopical Society, new series, vols, xviii.-sxviii. (London, 1878-87) : Bell. "On the Arrangements and Interrelations of the Class- es of the Echinodermata," Annals and Magazine of Xatural History, series vL, vol. vii. (London, 1891); Ludwig, Morphologische Stiidien an Kchinodermen (Leipzig, 1877-82); Xeumayr. Die Stiimme des Thicrreichcs (Vienna and Pragiie. 1SS9). See, also, the works cited under the articles on various classes of echinodcrms above referred to. .ECHINOIDEA. ek'i-noi'dA a (X'eo-Lat. nom. pi., from Ok. ^x'""'- cchinns. hedgehog + elSos, eidos. form). One of the five classes of Echino- dermata (q.v.). containing the sea-urchins and their kindred. It is sulidivlded into four orders: (1) Palajo-Echinoidea, all fossil; (2) Regularia, the typical globular echinoids or sea-urchins; (3) Clypeastridea, the llattened cake-urchins and sand-dollars: (4) Spatangoidea, the cordate heart-urchins. For further details of existi;ig fuiiMS, see SK.-fBCinx. ECHIUM, ek'i-nm. See Viper's Btgloss. ECHIURIDA, ek'i-u'rlda. An order of anne- lids. See An.NVL.TA. ECHMIADZIN, 6ch'me-ad-zen'. See Eicii- MIAll/lX. ECHO (Lat., from Gk. 'IIx*, (rom-iixor, cchos, sound). A personification in Greek mythology. Acconling to the legend, the nymph Echo, by her talking, detained Hera when .searching for Zeus among the mountain nymphs. .Vs a punish- ment the goddess deprived her of the power of speech unless first spoken to, when she was compelled to rejdy. The love of Pan for Echo was also celebrated by later poets, .ccording to Ovid, the nyinph Echo, having conceived a hopeless passion for Xareissus, pined away until only her voice remained. A portico at Olympia, where there was a seven-fold echo, was called by the nymph's name. ECHO. .Sound is produced by longitudinal waves or vibrations of the air or other medium through which it travels, and these waves on striking a surface are reflected according to the laws of reflection. A sound thus reflected is termed an echo, and the rule that the angle of incidence nuist equal the angle of reflection holds good, as in the case of light and other forms of wave-motion. If the sound is reflected by an obstacle at right angles to the direction of propagation, the echo returns to an obsen-er at the place where the soimd originated. This phenomenon enables one to ascertain the dis- tance to a clifT or other surface from which an echo is obtained, and is made use of by naviga- tors when approaching, in a fog. a shore with cliffs. Knowing that sound at ordinary tempera- tures travels with an apprn.ximate velocity of 1125 feet per second, by multiplying this figure by the time between the sound — that of a steam whistle for example — and the perception of the echo, we obtain the distance to the cliff and back. Reflection also takes place from the surface of a cloud, as is the case with thunder, and an uneven surf;icc .such as that iiresented from the edge of a wood, which often will furnish excellent echoes. ECHO, IN Mrsic. (1) A subdued repetition of a phrase. (2) In large organs there is a separate set of pipes, placed at a distance, so as to produce the effect of an echo. There are separate stops and generally also a special manual. ECHO CANON. . long and deep gorge in northern Ltah, on the Union Pacific Railroad (Map: Utah, B 1). It is aliout 25 miles north- east of Salt Lake, and is remarkable for its echoes and sublime .scenery. The sides of the canon are of bare rock and almost vertical. Owing to erosion, many of the rocks have as- sumed curious shapes. ECHTER, C-K'ler, MirH.Ei. (1812-70). A Ger- man painter. He was born in 'Munich, received his artistic training at the academy (here, and assisted Julius Schnorr von Karolsfcld (q.v.) in the dei'oration of the sallc dcs files of the royal palace at ilunich with nineteen wall paint-