1911] Watson: The Genus Gyrocotyle. 415 



2. A proximal ring commissure directly connected with the 

 posterior margin of the ganglionic knots. 



3. A distal ring commissure, connected with the proximal 



ring by eight connectives. 



4. Anastomoses between these connectives in the lateral walls 

 of the funnel. 



5. Eight branches running posteriorly from the distal ring 

 commissure into the folds of the terminal rosette. 



The main longitudinal stems lie as above noted in the dorsal 

 half of the central region. At a point just posterior to the tope. 

 close to the wall of the funnel, each stem enlarges to form a 

 ganglionic knot (pi. 35, fig. 17). These knots are connected 

 dorsally by a transverse bridge which is fairly large laterally, 

 but narrows to the merest thread in the median region, not dis- 

 tinguishable with a magnification of less than 300 diameters. 

 The ganglionic knots at the ends of this bridge commissure pass 

 diagonally across the lateral walls of the cavity. This forms the 

 "bow-commissure" of Spencer. Each ganglionic knot divides 

 into two main branches, a dorsal and a ventral, which pass 

 toward the median line to join similar branches from the opposite 

 side, thus forming the proximal ring commissure, lying aboul 

 half-way between the neck or sphincter region and the tope of 

 the funnel. It was probably the ventral half of this ring which 

 Spencer regarded as forming the "dorsal" region of his bow- 

 commissure, embracing the funnel. Lonnberg's "ventral" com- 

 missure was probably the dorsal half of this same ring, plus the 

 lateral ganglionic knots of the posterior commissure, the half- 

 ring and knots being connected by one of the primary lateral 

 connectives to be described later. The middle third of the dorsal 

 posterior bridge commissure is so delicate that it is easily oxer- 

 looked. However, the continuity and independence of both the 

 dorsal commissure and the dorsal half of the ring can be easily 

 demonstrated in serial sections with a magnification of about 300 

 diameters. 



In the neck or sphincter region there is formed a second ring 

 which completely encircles the posterior margin of the funnel at 

 the base of the frills. This posterior ring is connected with the 

 proximal ring by eight connectives i lat. long, conn., pi. 35, fig. 



