Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/78

forms greatly increases in the Arctic Sea. The tropical waters abound with lustrous and splendidly tinted specimens, especially amongst the Amphinomidse. The borers in shell, limestone, coral, and Melobesia, seem cosmopolitan, and the swimming Tomopteris is likewise widely distributed. The forms frequenting the bottom of the sea live in mud or sand, or lurk under stones, in chinks of rocks, shells, and seaweeds. Many specially affect mud or muddy sand, e.g., the Lumbriconereidae, Nephthydidrse, Glyceridse, and the Terebellidse ; while some prefer hard or stony ground, e.g., the Polynoidte and Sigalionidas. Between tide-marks they abound in fissures of rocks, under stones in pools, under tangle-roots, and in sand or sandy mud. Many live in captivity several years, but the duration of their exist

ence generally is unknown.

FIG. 11. Pectinaria bdgricrt,Pall. (Af .eraialmgren.)

1 IG. 12. Tube of fig. 11, partially shaded.

Tubicolar Polychaeta occur in various strata, from the Lower Silurian upwards, and Serpulites even appear in the quartz of Durness. Many of the tracks and burrows re ferred to the group (Polychseta) are involved in consider able doubt; but the Uunicites, Lumbriconereites, and Merin- gosoma, from the Solenhofen rocks, are satisfactory evi dences of fossil forms. The arrangement of the apertures of Arenicola didyma, from the Longmynd, in pairs is peculiar.

FIG. 13. Ckloeia.

FIG. 14. Hesione splfndida, Sav. (After Savigny.) navtiloidei, La-

In regard to beauty of form and colour, complex structure and wonderful habits, the Polychaeta are not surpassed by any invertebrate class. The splendid bristles of the Aphroditidae, constantly glistening with all the hues of a permanent rainbow, the brilliant tints of the Phyllo- docidoo, Hesionidge, and Nereidse, and the gorgeous branchial plumes of the Terebellidae, Sabellidee, and Serpulidee, can only be compared with the most beautiful types of butter flies and birds.

The class Annelida has been divided into the sections Branchiata and Abranchiata, the former comprehending the Polychaeta, the latter the other groups ; but this does not always hold good, since many Polychaata have no branchiae The latter, again, have been separated into the Dorsibranchs and Cephalobranchs, the former corresponding to the Maricola, Errantia, or Nereidse of others, the latter to the Tubicola fl -^}?; orSedentaria. G rube s divisions, Rapacia and Limivora, are based on the nature of their food. In the present state of the department it will suffice to indicate the following families (chiefly after Malmgren) under which the Annelida Polychreta have been ranged, and to refer for further information to the Annelides of De Quatrefages, the Familien of Grube, the Chcetopoda of Ehlers, the Annelides Chetopodes of Claparede, the British Museum Co.talogue by Johnston and Baird, and the various works of Kinberg and Malmgren : EUPHROSYNIDJS, AMPHINOMID.E (fig. 13), APHRODITIDJE, POLYNOID.E, ACCE- SlGALIONIDyE, NEPHTHY- PHYLLODOCID^:, HESIO- NID.E (fig. 14), ALCIOPIDJE, To- MOPTERID.E (provisionally), SYL- LID^;, NEREIDS (fig. 1 ), STAURO- CEPHALID^E, LUMBRICONEREID/E, EUNICIDJE (fig. 4), ONUPHIDID.E (fig. IO),GONIADID.E,GLYCEBID^;, BREGMID.E,TELETHUSID. : E(fig. 20), STERNASPID.E, CH.ETOPTERID.E, (fig. 21), CIRRATU-

, CAPITELLID.^:, MALDANID^;

(fig. 9),AMMOCHARID^, HERMEL- HOJE, AMPHICTENID.E (figs. 11 and 12), AMPHAKETID.E, TERE- BELLID^:, SABELLID.E (fig. 1C), ERIOGRAPHID^, and SERPULID^E (fig- 15).

II. The A. Oligochæta are annelids without tentacles, cirri, or specialised branchial processes. Bristles, variously grouped, from two to eight and upwards in each transverse series. They are hermaphrodite, and the young undergo no metamorphosis.

The body is enveloped in a delicate cuticle resembling that of the Polychaeta, and pierced by many pores. Under neath is a cellulo-granular hypoderm, with numerous glands. The setas are simple, bifid, or hair-like. The muscular layers are an external circular, and an internal longitudinal, marked by the bristle sacs. The foregoing tissues enclose a perivisceral space, with the usual septa and the charac teristic corpuscles in a coagulable lymph, which performs important functions in the economy.

The circulatory system consists essentially of a dorsal trunk situated over the digestive chamber, carrying the