

472 



J. F. ILLINGWORTH, 



A commissure connects these two branches above the rectum. Each 

 branch continues forward in an afferent branchial sinus, giving off 

 many small nerves to the gill plates. The anal end of the rectum, 

 also receives two small nerves from this same source. From the left 

 posterior angle of the visceral ganglion a nerve is given off to the 

 stomach (G.as) which forms an anastomosis, lying just under the 

 outer coat of this organ. 



The gill ganglia 

 are almost spherical in 

 shape, and each is situated 

 in the anterior half of 

 an efferent branchial sinus 

 (Fig. 0). Four nerves are 

 given off from each 

 ganglion, the largest one 

 of which (Os.g) runs for- 

 ward in the efferent sinus. 

 It is really a ganglionic 

 chord, and lies just within 

 the osphradium which re- 

 ceives a great number of 

 short nerves from it. 

 Fig. 5 is a cross section 

 of the osphradium and 

 its ganglion taken through 

 one of the nerves that 

 unite them. The gan- 

 glionic cells (G. c) are 

 seen in the periphery, and 

 are also especially abun- 

 dant among the columnar 

 epithelial cells (C.ep) of 

 the osphradium. The only 



Fig. O. Nerves of ctenidia. A anus, Vis. g visceral 

 ganglion , Af afferent branchial sinus , Uf efferent 

 branchial sinus, Exr external papilla right nephridium, 

 G.g gill ganglia, Mf nerve to mantle fissure, Os.g os- 

 phradial ganglia , E rectum , Ra reno-anal nerve, 

 1 connective to anterior mantle nerve, S nerve to 

 papilla right nephridium, 4 nerves to ventricle, 5 con- 

 nectives to intestinal ganglia, 6 anastomosing nerves 

 to auricles. 



external indication that 

 one sees of this sense organ is a slightly depressed line of a yellowish color 

 (Fig. 12 Os) running along the outer portion of the efferent branchial 

 sinus. In section we find that the columnar cells of this region are 

 similar to those of other parts of the mantle cavity, except that they 

 are considerably larger. Several large multipolar nerve cells (Mp) 

 were found in sections of this ganglionic nerve. The next largest 



