TEREBELLIDAE. 419 



on which biramous parapodia are borne, and a narrower abdominal region 

 bearing only the neui'opodia or uncinigerous tori, or rarely also bearing capillary 

 setae (Aphlebina). The thorax, however, is less differentiated than in the 

 Ampharetidae. The colors are often bright and variegated. 



The prostoinium bears filamentous tentacles that are more or less long and 

 numerous and that arise from a lobe or lobes of varied form and size. No 

 tentacular cirri. 



Branchiae may be either present or absent. When present there may be 

 one, two or three pairs, and these maj' be of the cirriform, subulate, arborescent 

 or pectinate type. 



The notopocUal thoracic setae are capillary and generally limbate, with 

 the border sometimes in part denticulate or serrulate. The crochets may be 

 of varied form, avicular, pectiniform, rostrate or acicular, with either all of 

 one kind or with one kind anteriorly and another posteriorly. Rarely no setae 

 at all occur (Hanchiella). 



The aUmentary canal shows a division into pharynx, oesophagus, stomach, 

 and intestine. But unlike the stomach of the ampharetids, that of the members 

 of this family shows a division into a chitinous stomach and a glandular stomach, 

 with no trace of anterior or internal caeca. 



The terebellids are normally tubicolous, though some adults may at times 

 leave thek tubes and swim freely through the water, as noted by Michaelsen 

 (Jahrb. Hamb. wiss. anstal., 1892, 9, p. 110) in the case of Nicolea venustula 

 Montagu. Free swimming young forms have more often been noted; and St. 

 Joseph has recorded (Ann. sci. nat. Zool., 1899, ser. 5, 10, p. 185, pi. 6, fig. 20-24) 

 a highly interesting case of pregenesis in a free-swimming postlarval stage of 

 his Amphitrite praecox. This j'^oung form has long setae of the general type of 

 the natatory setae of the epitokous stages of various other annelids, and at the 

 same time bears eggs. As pointed out by Gravier (Nouv. arch. Mus. hist, nat., 

 1908, ser. 4, 10, p. 211) this case of pregenesis, apparently compUcated by epitoky, 

 is intermediate as to date of appearance betw^^en the pregenesis noted in ciliated 

 larvae of Paractius, Ophryotrocha, and WarteUa and the normal case. 



The tubes of the terebelhds consist of a lining membrane, secreted by the 

 animal, to which become consolidated mud, sand, spicules of sponges, fragments 

 of shells, or other material from the surroundings. The tubes are large in pro- 

 portion to the size of the contained anunals. The tubes ordinarily occur in 

 mud, or sand more or less mixed with mud, though some are found in solid cal- 

 careous masses, which it has been suggested they penetrate by means of an acid 



