38 PHYSIOLOGY OF THE INVERTEBRATA. 



the stomach a narrow intestine passes to the anus, which is 

 situated dorsally. The stomach is produced into a number of 

 lateral cjeca, or diverticula. 



The alimentar}'- canal of McdacohdcUa is " a simple tube 

 bent several times upon itself." 



(4) The Oligocluvta — The earthworm and certain fresh- 

 water worms belong to this order. The body is elongated, 

 rounded, and segmented. The mouth is a small aperture, 

 leading into a buccal cavity, and into which true salivary 

 glands open. This cavity or sac passes into a pharynx, 

 which is continued into a straight oesophagus bearing three 

 pairs of lateral diverticula (the oesophageal glands). About 

 the region of the fifteenth segment the CBSophagus opens into 

 a dilated portion of the alimentary canal called the crop or 

 proventriculus. The crop leads into the gizzard or stomach, 

 which is provided with strong muscles. The gizzard is 

 succeeded by the intestine, which terminates in an anus. 



(5) The Poljiduvfa. — In this order the alimentary canal 

 " rarely presents any marked distinction into stomach and 

 intestine." The mouth opens into a muscular pharynx, which 

 is capable of being protruded as a proboscis ; and in Pol/pwe 

 and other genera the proboscis is provided with papillae and 

 chitinous teeth. The pharynx leads into a straight tubular 

 intestine. In certain genera of the PoIi/cha''ta there are long 

 CEeca which form lateral appendages to the intestine. The 

 function of these cfeca is of a pancreatic nature ; while the 

 pair of glandular organs appended to the base of the proboscis 

 in Nereis are true salivary glands. The anus, in many 

 Annelids, is not terminal, but is situated in the centre of a 

 raised papilla on the dorsal side of the animal. 



The Nematoscolices. 



This class of the Arthrozoic Series is divided into three 

 orders : the Nematoidca, Nematorhyncha, and Acantho- 

 cephala. 



