(114) 

 of insertion of the collar trunk mesentery and si ve rise to a 

 collar nerve ring. The nerve fibers from the edge of Che pre- 

 oral hood do not pass up to the gaiiglion from the point of at- 

 tachment "f the hood on to the collar wall as Masterrrian has de- 

 scribed^l^ut triey make a sharp turn running posteriorly arid 

 obliquely alon^ the lateral and ventral wall of the collar, where 

 t' le y form two definite nerve tracts which become lost in the 

 region of the collar nerve ring. While there may be nerve fi- 

 bers passing from the gajjglion out in all direct ioiiS over the 

 sur-^ace of the hood, 1 have not beeii a.ble to make ti:emout, nor 

 do 1 find any definite nervous tract ninning along the dorsal 

 or ventral v/all of tlie trunk segment. 



There is one pair of retractor muscles extending from the 

 region of the ganglion to the collar walls in the region o"f* t,he 

 first and second pairs of tentacles ar^ beside these in one Ac- 

 tinotrocha that I have examined, there is another pair extending 

 from the sides of the gaiiglion to the veritral wall o -^ the hood. 

 In this latter Actinotrocha there is an extensive layer of mus- 

 cle fibers in the wall o^ the hood and also a ring of fibers 

 around the edge of the latter, A pair of longitudinal muscle 

 tracts extend from the region of the ganglion alon,: the dorsal 

 wall of the Actinotrocha to the perianal ring ana there is a sim- 

 ilar pair of rrd,cts extending along the ventral wall of the col- 



