Echiuroidea

ECHIUROIDEA. The echiuroids are a small group of ex clusively marine animals which live in tubes or galleries in the rock. They are of moderate size (Ikeda is recorded with a length of two metres) with a sac-like body surmounted by a large pre oral lobe or proboscis, with which they explore their surroundings in search of food. In almost all species there is a pair of bristles, strictly comparable with the bristles of the annelids or segmented worms, on the ventral surface a short distance below the mouth; by means of these the animals can enlarge the walls of their burrows. They can also drag themselves from place to place by fixing the proboscis to a sta tionary object and by its contrac tion drawing the body forward. Echiurus is capable of swimming freely, which it probably does at night ; this would account for the occurrence in certain places of large numbers of these animals thrown up on the beach on the morning after a storm.

Phylogeny.

The precise re lation of the echiuroids to other animal groups still remains obscure. Many authorities con sider them closely allied to the annelids, but certain primitive features in their development make it preferable to regard them as an early offshoot of the same branch as that which gave rise to the annelids rather than as members of that group that have lost their segmenta tion.

Anatomy.

T h e body-wall consists of a cuticle, glandular epidermis, a cutis and three layers of muscle. There is a roomy body cavity or coelom which municates with the exterior by a varying number of nephridia or ducts, which serve both for excretion and for the passage of the genital products. The coelom is filled with corpuscles and in some species also contains globin. The ciliated proboscis leads by a simple mouth into the alimentary canal, which is divided into regions according to their function in digestion. The mid-gut is provided ventrally with a ciliated groove and a collateral intestine. From the rectum two large sacs are given off which communicate with the coelom by a number of ciliated funnels and to the exterior by the terminal part of the rectum. These are absent in Hamingia sibogae.

Except in Urechis, there is a closed vascular system, consisting of a dorsal and a ventral vessel joined medially by the neuro-intes tinal vessel and in front by a vessel which loops round the proboscis. The gonad is a solid cord of cells on the posterior extremity of the ventral vessel, and the genital products develop free in the coelom and escape by way of the nephridia. The nervous system consists of a ventral nerve cord without ganglia, from which the nerves come off at irregular intervals. In front there is a large nerve ring looping round the proboscis.

Embryology.

The larva is a trochophore possessing transi tory evidences of segmentation in the arrangement of the pig ment and of the cilia. The development is characterized by the enormous elongation of the pre-oral lobe.

Classification.

The echiuroids may be divided into two families, the Echiuri dae in which the male and female are simi lar and the Bonelliidae in which the male, lacking both mouth and anus, is a minute parasite on the female. All the Echiuridae except Thalassema and its allies have bris tles round the anus. Nearly all the Bon elliidae have paired ventral hooks and a bifid proboscis, except Hamingia which has no ventral hooks and an undivided pro boscis.

Habits.

Echiurus forms a tube ce mented with mucus; Thalassema and Bon ellia live in holes in the rock. In Bonellia the sex of the adult depends on the mode of life of the larva. The larvae that live a free existence unat tached to an adult female develop normally into females. Those that are to become males settle on the proboscis of an adult female ; after three days they creep inside, develop male character istics and eventually come to rest in the uterus of the female. The determining factor seems to be a water-soluble substance secreted by the proboscis and the gut-wall of the female ; for Baltzer by feeding an extract of these organs to the free-living larvae has obtained a high percentage of males, which, however, do not reach full development. By removing the larva from the proboscis of the female before the completion of the sex-determining process intersexes can be produced. In Pseudobonellia there is a special tube in the body wall in which the male lives.

See W. K. Fisher and G. E. MacGinitie, "The Natural History of an Echiuroid Worm," Am. Mag. Nat. Hist. (1928). (C. C. A. M.) ECHMIADZIN, (I) a monastery in the Armenian S.S.R., in 4o° 12' N., 44° 19' E., the seat of the Catizolicus or primate of the Armenian church. It is situated close to the village of Vagarshapat, in the plain of the Aras, 2,84o ft. above the sea, 12 m. west of Erivan and 4o north of Mount Ararat. The monastery comprises a complex of buildings, surrounded by brick walls 3o ft. high, which with their loopholes and towers present the appearance of a fortress. Its architectural character has been considerably impaired by additions and altera tions in modern Russian style. On the western side of the quadrangle is the residence of the primate, on the south the re fectory (1730-1735), on the east the lodgings for the monks, and on the north the cells. The cathedral is a small but fine cruci form building with a Byzantine cupola at the intersection. Its foundation is ascribed to St. Gregory the Illuminator in 302. Of special interest is the porch, built of red porphyry, and profusely adorned with sculptured designs somewhat of a Gothic character. The interior is decorated with Persian frescoes of flowers, birds and scroll-work. It is here that the primate confers episcopal consecration by the sacred hand (relic) of St. Gregory; and here every seven years he prepares the holy oil which is to be used throughout the churches of the Armenian communion. Outside the main entrance are the alabaster tombs of the primates Alex ander I. (1714), Alexander II. (1755), Daniel (1806) and Narses (1857), and a white marble monument, erected by the English East India Company to mark the resting-place of Sir John Mac donald Kinneir, who died at Tabriz in 1830, while on an embassy to the Persian court. The library of the monastery is a rich store house of Armenian literature (see Brosset's Catalogue de la bibliotlieque d'Etchmiadzin, St. Petersburg, 184o). Among the more remarkable manuscripts are a copy of the gospels dating from the loth or 1 i th century, and three bibles of the i3th cen tury. A type-foundry, a printing-press and a bookbinding estab lishment are maintained by the monks who supply religious and educational works for their co-religionists.

To the east of the monastery is a modern college and seminary. Half a mile to the east stand the churches of St. Ripsime and St. Gaiana, two of the early martyrs of Armenian Christianity; the latter is the burial-place of those primates who are not deemed worthy of interment beside the cathedral. From a distance the three churches form a fairly striking group, and accordingly the Turkish name for Echmiadzin is Uch-Kilissi, or the Three Churches. The town of Vagarshapat dates from the 6th century B.C. ; it takes its name from King Vagarsh (Vologaeses), who in the end century A.D. chose it as his residence and surrounded it with walls. Here the apostle of Armenia, St. Gregory the Illumi nator, erected a church in 309 and with it the primacy was associ ated. In 344 Vagarshapat ceased to be the Armenian capital, and in the 5th century the patriarchal seat was removed to Dvin, and then to Ani. The monastery was founded by Narses II., who ruled ; and a restoration was effected in 618. The present name of the monastery was adopted instead of Vagarshapat in the loth century. At length in 1441 the primate George brought back the see to the original site.

(2) An administrative district of the Armenian S.S.R., with an area of 3,009 sq.km., and a population (1926) of mainly rural. Vagarshapat (see above) is the centre, pop. (1926) 8,035. The district suffers severely from drought, but a scheme of irrigation is now being inaugurated which should greatly in crease the cotton production of the region.