1 64 



ZOOLOGY 



into the body-cavity. At their upper ends the sacs are attached 

 to the body-wall, and open to the exterior a little in front of 

 the level of the anus. Each sac consists of two portions : a 

 posterior glandular part Uned by large glandular cells, which 

 give off vesicles containing their excretion, and a muscular 

 non-glandular anterior half, which opens both on to the 



Pig. 105. — Diagram showing 

 relation of nervous system, vas- 

 cular system, and oesophagus in 

 Phymosoma varians. Partly 

 after Selenka. 



1. The brain, represented rela- 



tively too small. 



2. Nerves to skin of preoral lohe. 



3. Lophophore ; each tentacle is 



represented by its blood 

 sinuses and its nerve. 



4. Blood sinuses of lower lip. 

 6. Oesophagus. 



6. Dorsal blood-vessel. 



7. Ventral nerve cord. 



exterior and into the coelom. The opening iato the latter 

 space is situated close to the external opening, and is guarded 

 by a frilled, funnel-shaped Hp, thickly cihated. The wall of 

 the organ contains many muscle fibres, and it is capable of 

 considerable change of form. 



The nervous system consists of a bilobed brain in con- 

 tinuity with the epidermis of the concavity of the lophophore 

 (Fig. 103). It gives off a pair of lophophoral nerves, which 

 run along the base of the tentacles, sending off a nerve into 



