236 



NATURAL BIS TOR I'. 



great tentacles projecting from it, has on certain segments a branchial cirrus springing from the back, 

 and as long PS half the diameter of the body. * 



The family Sternaspidae have very short bodies, the anterior region thick and carrying three 

 rows of setae, and there is a corneous shield near the end beneath. On the other hand, the Pherusidie 

 have long cylindrical bodies with two strong forked tentacles 011 the head, and the buccal papillae 

 and branchial filaments are retractile. The first or second segments cany very long setae, and in some 

 the branchial organs are on a peduncle. Trophonia plumosa is one of them. 



A great host of Tubicolae live upon most shores, and have their tubes coated with broken shell, 

 gravel, or sand, and membranous within and open at both ends. Some have their tubes visible and 



1 always covered with water, and others 



bury them in sand or mud, raising the 

 orifice a little above the earth. These 

 work between tide marks. Many live 

 in groups, and are said to be gregarious, 

 and their tubes are very fragile, being 

 composed of sand. 



All these tube-makers belong to a 

 large family, the Terebellidae. The 

 animals are worm-shaped, thick in front 

 and narrow behind. The cephalic region 

 is not distinctly separated from the 

 buccal ring, and often has a collar. 

 There are numerous tentacles, filiform 

 in shape, and divided into two groups 

 around the mouth. There is no pro- 

 boscis, and there are branched or 

 comb-shaped branchiae on some of the 

 anterior segments. In some genera 

 there is a transverse row of stiff golden 

 bristles on the dorsal margin of the post- 

 occipital segment. The segments are 

 very numerous in some, and the worms 

 attain the length of eight to nine inches, 

 or more. The colouring is very pretty, 

 and the shape of the setae is lanceolate,, 

 hooked, siphon- shaped, and knobbed. 



The larvae of the Terebellidae are 

 covered with cilia, except at both ends, 



where several bands of cilia become apparent ; they have auditory sacs. This is the case in Tere- 

 bella conchilega. When growth has proceeded so as to develop feet, the cephalic lobe becomes 

 distinctly visible, and it has two eyes and one tentacle. At first there are only single setae, but 

 when the Terebella begins to construct its tube, forked setae and branchiae appear. Some of the 

 larvae crawl on the sea floor, and the others swim freely. The full-grown worms have the tubes- 

 made up of slimy matter which has entangled pieces of sand and stone ; and one forms a case of 

 loose sand large enough to permit it to turn within and to use either end for the projection of 

 its tentacles. A Scottish species covers its body with a web made up of the finest threads, almost 

 invisible from their slenderness and extreme transparence. The web extends far beyond the 

 body, and puts one in mind of that of a Spider. Dalyell states that a specimen nine lines long, 

 had a web covering an ai*ea fifteen lines square. The threads are fixed as high as the length of the 

 worm, and below also, and ai*e secured to neighbouring objects. The web serves to support the ova. 

 Moreover, this weaving species constructs a semi-cylindrical shell of sand or mud, but it is not large 

 enough to include the body and head perfectly, so it is abandoned very constantly for a new one. 



* Leucodora ciliata. 



TEKEKELL.V UMMALINA. 



