I40 



ZOOLOGY 



and an intestine. On the ventral wall of the oesophagus a 

 U-shaped tube opens ; one limb of this tube is enormously en- 

 larged, and is very muscular. A somewhat 

 —^ similar stomodaeal musculature occurs in 

 the pharynx of most Chaetopods, and would 

 seem to be comparable to the odontophore 

 of Molluscs, and with the ventral part 

 of the muscular pharynx in Turbellarians. 

 The intestine is moniliform, there being a 

 constriction between each segment. It is 

 supported by the transverse septa and by 

 median dorsal and ventral mesenteries (Fig. 

 90). Its lumen is ciliated. The anus is 

 terminal. 



The vascular system consists of a 

 median dorsal vessel, which sends a 

 branch along each tentacle. Other 

 branches bring the colourless blood back 

 from the tentacles, and these then fuse to 

 form the median ventral vessel. Certain 

 lacunae between the epithelial cells of the 

 intestine and its musculature appear to 

 Fig. 88.— View of a ne- supply the dorsal vessel with the fluid it 



phridium oiProtodrilus contains. 



Leuckartii. After Hat- mi ' i ■ t • ,. • i 



schek. ihe nephridia consist ot an mternal 



1. Internal opening funnel (Fig. 88), from the edge of which a 



2. E^ie'nfiTpeZg. ^^^ge ciHum_ depends into the lumen of the 



3. Cilia of anterior ring tube which is ciliated; this passes through 



of the segment. , • t -l • j j5 n 



4. Cilia of posterior ^ scptum, as m Lumhncus, and finally 

 ring^ of the seg- opens to the cxtcrior on the lateral line. 



The nervous system remains in the 

 skin (Fig. 90) ; it consists of a cerebral 

 mass, with circum-oesophageal commissures, which pass into 

 two ventral cords. The latter are separated from one 

 another by the ventral groove, but are connected by trans- 

 verse commissures. 



Protodrilus is hermaphrodite, Polygordms dioecious; the 

 ovaries lie in the first seven -segments. The ova are derived 

 from some of the cells lining the coelom in the neighbourhood 



ment. 

 Septum. 



