232 LECTURE XI. 



e. g., there are four on one side and three on the other side of the 

 protractile pharynx : in Lumbrinereis there are eight jaws, and in 

 Aglaura nine. These jaws are sharp-pointed and dentated on their 

 inner border, and, when the pharynx is everted, they project exter- 

 nally, and can be used as prehensile organs. The Tubicola are 

 edentulous. 



The obliquity of the constrictions of the alimentary canal in the 

 Sabella pavonina* give it the appearance of being a long and nari'ow 

 tube disposed in a series of close spiral coils ; but it is merely saccu- 

 lated. In most other tubicolar anellids the intestine is less constricted 

 than in the Sabella ; and in Amphitrite it is uniform, irregularly con- 

 voluted, and loosely suspended in the abdominal cavity. 



In the TerebellcB nebulosa and conchilega the wide and long oeso- 

 phagus is coated by a yellow glandular mass, and is separated from 

 the slightly sacculated yellow gastro-intestinal tube by an elongated 

 colourless gizzard. In the Hermella there is a short oval dilatation 

 or stomach between the oesophagus and intestine. 



In the sand- or lug-worm (^rewecoZa) the gastro-intestinal canal (Jig. 

 106.) commences at the termination of the oesophagus (b) by a sudden 

 dilatation, into which two caecal glandular pouches (c) pour their 

 secretion : the rest of the canal is simple in its outward form ; but 

 its walls are thickened by a stratum of minute secerning cells (d), 

 which prepare a greenish-yellow fluid. The oesophagus can be 

 everted and protruded ; the sand is seized and swallowed as the worm 

 bores its way ; the organic particles are assimilated as the earthy 

 medium traverses the digestive canal, and it is finally rejected in the 

 form of the sand coils, which betray the retreats of the " lugs " on 

 the sea-strand. 



In most of the Errantia there is no distinction between stomach 

 and intestine ; this runs straight to the terminal vent in Eunice and 

 Amphinome, as in Arenicola : in Cirratulus it takes a spiral course ; 

 and it is irregularly convoluted in Ammotrypane. In some Nereids 

 the canal is provided with lateral pouches, a pair of which, in Nereis 

 proper, open into the compartment of the canal which answers to the 

 stomach. The intestinal canal is lined by a ciliated epithelium in all 

 anellids. In the Aphrodita aculeata the part homologous with the 

 projectile proboscis of the Nereids is converted into a kind of gizzard, 

 by the thickening of the muscular coat. The alimentary canal, con- 

 tinued from its posterior extremity, bends forward at first for half 

 the length of the gizzard, a disposition which indicates the occasional 

 protrusion of this part. The canal then bends backwards, and is 



* No. 441. 



