X. Phoronida and Actinotrochia 



Wright in 1856 described the first species of Phoronis. Dyster, 

 1858, suggests two oesophageal gangha. He found that the crea- 

 tures were not particularly sensitive to light. I have a reference 

 to a paper by Kowalevsky, 1861, on the anatomy and development 

 of Phoronis, but as I have not seen it or a review of it I do not know 

 how much the nervous system is considered. 



Caldwell's publication of 1883 is the next paper of importance. 

 He describes the nerve processes in connection with the ectoderm; 

 both fibers and ganglion cells occur in the ectoderm. There are 

 concentrations of the nervous tissue about the mouth to form a 

 post-oral nerve ring; the anus is outside of this. The ring forms 

 a line along the base of the tentacles formed like a horse shoe. In 

 front of the ring is a pair of sense organs, the ciliated pits in the 

 concavity of the lophophore on either side of the anus. There is an 

 epithelium here with sense cells, ganglion cells and nerve fibers. 

 The nervous system is further continued on the left side from the 

 dorsal part as a cord or strand just outside the basement membrane. 



Mcintosh, 1888, in P. buskii describes a similar epidermal sys- 

 tem concentrated about the mouth to form a post-oral nerve ring 

 with the anus outside. The ring follows the line along the base of 

 the tentacles and to the "ciliated pits" or concavity of the lophophore 

 on either side of the anus. The nervous system has sense cells 

 and ganglion cells and nerve fibers. On the left side is a cord 

 through the body. The left longitudinal nerve tube or tubes of 

 Caldwell is not described. 



Andrews, 1890, in a new species describes the "glandular pit" 

 of the lopophore and a large "nerve rod" on the left side, solid and 

 surroundecl by epidermal cells. It seems to have a fibrillated or 

 possibly only a coagulated structure. The rod extends through a 

 considerable distance and ends in a peculiar ring of epidermal nerve 

 substance about the mouth. At this region there are two symmet- 

 rically placed nerve rods but the right is short. 



Benham, 1889, finds the nervous system immediately below the 

 epidermis as Caldwell was first to observe. Passing aborally from 

 the lopophore ridge the basement membrane is seen to separate 

 from the epidermis by a narrow ground substance not readily 

 stained. In this granular substance are a few rounded nuclei be- 

 longing to small nerve cells. Fibers are also found coming from 

 the epithelial cells of the surface. This nerve band follows the 

 ridg« of the lophophore rassing around on the oral side and curves 

 at the side of the nephridial ridges following the spiral course of the 

 lophophore. It always keeps along the outer edge of the tentacles. 

 From this band nerve tissue goes to each tentacle passing along its 

 inner surface. A nerve goes to each nephridium and a nerve layer 

 to the epistome, this being the only dorsal part of the nervous 



