TWO AQUATIC OLIGOCEUETES. 



37 



The minute structure of the setigerous organs is the same 

 as in L. gotoi. 



3. Aliment aky system. 



The mouth lies on the ventral side of segment I, and is 

 continued directly into the buccal cavity. The latter is flattened 

 dorso-ventrally and opens into the pharynx at the middle of 

 segment II, with a constriction between them. 



The pharynx reaches to the end of segment III. It is well 

 differentiated by the development of the pharyngeal glands. It 

 is semicircular in cross-section ; the lumen is concave ventrally 

 and there is no median inlet. The wall of the pharynx consists 

 of two layers : an inner of long cylindrical, ciliated, endodermal 

 cells, forming a pad -like projection into the pharyngeal cavity on 

 the ventral side, and a thin outer of connective tissue containing 

 feebly developed blood vessels and pretty well developed muscle 

 fibres. 



The pharyngeal glands are arranged in six longitudinal rows 



on the dorsal side of 

 the pharynx, begin- 

 ning directly behind 

 the brain and extend- 

 ing to the middle of 

 segment III, with the 

 exception of the two 

 lateral or outermost 

 ones, which run back 

 into segment V; but all 

 open into the pharynx 

 in segment III. Each 

 lateral gland presents 

 Fig. 27. a dorsal swelling in 



L. willexji. Cross section through segment III, to show Segment IV and is 



the pharyngeal glands. xl50. ip-lateral line, sb-setiger- consideral)ly enlarged 



ous organ, sb' — cell of young setigerous follicle, nc — ventral ^ # 



nerve cord, pg — pharyngeal glands. at IDS lllllCl eilCl in 



1 ip 



