POLYCH.ETA, TUBICOL.E. 381 



tacular cirri upon the head (Captiibranchiata), of which one or 

 more may bear an operculum at its apex to close the tube (fig. 

 308). The parapodia are short, and are never used in swimming; 

 the notopodia usually carry hair-like setae ; the neuropodia are trans- 

 verse ridges with hooked setae or plates. Eyes are very frequently 

 absent ; in other cases they are present in pairs upon the head or on 

 the terminal segment, sometimes even on the branchial tentacles; 

 in the latter case they are very numerous. The body is often 

 divided into two (thorax and abdomen) or three regions, the seg- 

 ments of which are distinguished by their unequal size. The 

 Tubicolce live in more or less firm tubes which they construct for 

 themselves, and feed on vegetable matter which they procure by 

 means of their tentacular apparatus. In the construction of their 

 tubes the animals are assisted in various ways by the long tentacles 

 or branchial filaments of the head ; thus, for example, the Sabelliclce 

 are said to accumulate fine ooze at the funnel-shaped base of the 

 branchial apparatus by means of the cilia of their tentacles, to mix 

 it with a cement secreted by large glands, and then to transfer it to 

 the edge of the tube ; while the Terebellidce procure the grains of sand 

 for the construction of their tubes by their long and very extensible 

 tentacles. There are also boring Annelids, which pierce limestone 

 and mussel shells, like the horny Molluscs ; e.g., Sabetta saxicola, etc. 

 The development is simplest when the mother possesses a kind of 

 brood-pouch for the development of the young, e.g., Spirorbis spirillum 

 Pag., the eggs and larvae of which remain within a dilatation of the 

 opercular stalk until the young animals are able to construct a tube 

 for themselves. The free-swimming larvae of most Tubicolce, on 

 assuming the form of the worm, lose the ciliary apparatus, while 

 tentacles and parapodia make their appearance. In this condition 

 and sometimes surrounded by delicate membranes, they swim about 

 for some time longer, and, having lost their eyes and auditory vesicles, 

 gradually assume the structure and mode of life of the sexual animal 

 (Terebella). 



Fam. Saccocirridae. With two tentacles on the prac,stomium, two eyes 

 and the same number of ciliated pits. A single row of retractile parapodia, 

 furnished with simple setse, on either side of the segments of the body. Sacco- 

 cirrus papillocercus Bobr., Black Sea and Mediterranean (Marseilles). 



Fam. Arenicolidae. Prsestomium small and without tentacles. The pro- 

 boscis is beset with papillae. There are branched gills on the median and 

 posterior segments. The animals burrow in sand. Arcnicola marina Lin. 

 (A. piscatorum Lam.), North Sea and Mediterranean. 



Fam. Spionidae {Spiodcce). The small praestomium sometimes with tentacu- 



