378 WM. L. TOWER, 



Fig. 33), as in the case of the larger posterior lateral ganglion. In 

 structure it is like the posterior lateral ganglion , being composed of 

 a number of ganglionic cells embedded in a matrix of nerve fibres, 

 and the gangUonic cells are in every respect like those of the posterior 

 lateral ganglion. From the dorsal surface of the anterior ganglion 

 there arise, sometimes as a single trunk, two nerves which pass 

 medianward and dorsad and soon divide. One nerve passes laterad, 

 becoming the external genital nerve (n. gen. ex), and is distributed to 

 the region of the gonopore; the other passes inward, becomes the 

 internal genital nerve {n.gen.i, PI. 22, Fig. 6; PI. 23, Fig. 12; 

 PI. 26, Fig. 33; PI. 24, Fig. 27), and is distributed to the ovaries, 

 uterus, and other sexual organs of the region. There are a few 

 ganglionic cells along the course of these nerves, but no binding cells. 

 As far as I was able to discover the anterior lateral ganglion does 

 not become apparent until the proglottis is nearly mature, although 

 the two nerves are found in younger proglottides. This is due pro- 

 bably to the increased activity of those parts upon reaching sexual 

 maturity. 



There is a ventral commissure (PI. 22, Figs. 6 and 7 corns, v), 

 connecting the ventral surfaces of the posterior lateral ganglia of 

 each proglottis, and corresponding in size, shape and relations to the 

 dorsal commissure. These two commissures, together with the posterior 

 lateral gangha, form a complete nerve ring, embracing the two longi- 

 tudinal excretory tubes, and uniting the lateral nerve of one side 

 with its fellow of the opposite side. These two commissural nerves 

 are united to each other by means of two dorso-ventral connectives. 

 These connectives have the form of a loose band of nerve fibres that 

 passes dorso-ventrally from one commissure to the other close to 

 the median surface of the longitudinal excretory tube, and just behind 

 the union of the longitudinal and transverse excretory tubes {conH. d-v, 

 PI. 22, Figs. 6, 7 ; PI. 25, Fig. 28 ; PI. 26, Fig. 31). One of these con- 

 nectives with a small part of each of two commissures and the cor- 

 responding posterior lateral ganglion forms a complete ring of nerve 

 tissue that encircles the longitudinal excretory tube immediately behind 

 the transverse excretory tube. This dorso-ventral connective is like 

 the commissures in structure, being a band of loosely united nerve 

 fibres associated with a greater or less number of ganglionic cells. 

 A few nerve fibres are seen to pass off from these connectives, but I 

 have not been able to trace them to their terminations. 



The marginal nerve (PI. 22, Fig. 6 n.marg), arises from the an- 



