PHORONIDEA. 



543 



by cutaneous glands in the ante- 

 rior region. 



At the anterior or oral end of 

 the animal there is a horseshoe- 

 shaped lophophore entirely at- 

 tached to the oral surface (Fig. 

 438), no part of it projecting as 

 in fresh-water Polyzoa (see Fig. 

 441). The concavity of the 

 horseshoe is dorsal. In some 

 forms, e.g. Ph. australis, the two 

 ends of the horseshoe are curved 

 inwards into a spiral. The lopho- 

 phore carries two rows of hollow 

 ciliated tentacles, between which 

 is a groove leading into the 

 median mouth. Overhanging the 

 mouth on its dorsal side, i.e. 

 between it and the inner ten- 

 tacles of the lophophore, is a 

 laterally extended flap of the 

 body-wall the epistome (Fig. 

 438, ep.). The anus (an) is 

 dorsal and outside the lopho- 

 phore, at the summit of a median 

 longitudinal ridge (Rr\ on each 

 side of which there is a lateral 

 ridge (nr), each bearing at its 

 oral end a pore, the aperture of 

 a nephridium (neo). The row 

 of tentacles on the inner, i.e. 

 concave side of the lophophore, 

 is incomplete in the middle line. 



The body is elongated aborally, 

 and may attain a length of 

 6 inches. Development shows 

 us that the dorsal surface* is 

 the area between the mouth and 



FIG. 438. Diagram showing the anatomy of 

 Phoronis ; the left side of the body-wall and 

 the left half of the lophophore is supposed 

 to be cut away (after Benham) a oesopha- 

 geal mesentery ; af afferent blood vessel ; an 

 anus ; b right lateral mesentery ; ~bw body- 

 wall ; c rectal mesentery ; ef efferent blood 

 vessel; ep epistome; gl glandular ridge 

 and pit; int intestine; it inner series of 

 tentacles ; m mouth ; N nerve band ; 71.7-. 

 right nephridial ridge ; ne.d left nephridial 

 duct ; ne.f large funnel of the left nephri- 

 . diuni; ne.f small funnel of the left 

 nephridium ; ne.o right nephridiopore ; o 

 ovary ; oe oesophagus ; ot outer tentacles ; 

 R rectum ; R.r rectal ridge ; s transverse 

 septum ; st stomach ; tv tentacular vessel ; 

 T testis. 



* Caldwell states that the epistome is derived from the preoral lobe of the 

 larva, but this is inconsistent with the statement he also makes that the preoral 

 lobe is swallowed and digested at the metamorphosis. 



