376 



MANUAL OF ZOOLOGY. 



In all, or almost all, the Polyzoa in which this crescentic con- 

 dition of the lophophore exists, there is also a singular valve- 

 like organ which, springing from the anal side of the lopho- 



Fig. 199. i. Fragment of Flustra truncata, one of the Sea-mats, natural size. 2. A 

 single polypide of Valkeria, magnified, showing the orbicular crown of tentacles. 

 3. A polypide of Lophopus crystallinus, a fresh-water Poly2oon, highly magnified, 

 showing the horse-shoe-shaped crown of tentacles, a Tentacular crown ; b Gullet ; 

 c Stomach ; d Intestine ; e Anus j g Gizzard ; k Endocyst j / Ectocyst ; f. Funiculus. 



phore, arches over the mouth, and is termed the "epistome." 

 The only marine forms in which the lophophore is bilateral 

 are Pedicellina and Rhabdopleura ; the only fresh-water species 

 in which the lophophore is orbicular are Paludicella and Urna- 

 tella. 



The mouth conducts by an oesophagus into a dilated stomach. 

 In some cases a pharnyx may be present, and in others there 

 is in front of the stomach a muscular proventriculus, or giz- 

 zard. From the stomach proceeds the intestine, which shortly 

 turns forward to open by a distinct anus close to the mouth. 

 As the nervous ganglion is situated on that side of the mouth 

 towards which the intestine turns in order to reach its termina- 

 tion, the intestine is said to have a " neural flexure ; " and this 

 relation is constant throughout the entire class. 



Respiration in the Polyzoa appears to be carried on by the 

 ciliated tentacles,, and by the "perigastric space," which is 

 filled with a clear fluid, containing solid particles in suspen- 

 sion. A kind of circulation is kept up in this "perigastric 



