372 WM. L. TOWER, 



their course meet the two dorsal and two ventral longitudinal nerves. 

 Not only do fibres of these bands decussate with those of the longi- 

 tudinal nerves, but fibres also pass from commissure to longitudinal 

 nerve and vice versa. Along the course of these commissures there are 

 found a few ganglionic cells which are mostly of the unipolar type (PL 22, 

 Fig. 11). The position and appearance of these commissures reminds 

 one of the two hexagonal commissures found by Niemiec (1885) in 

 Taenia coenurus and T. serrata, with one of which they are pro- 

 bably homologous, although apparently they are less well defined 

 nerves than those in the species studied by Niemiec. 



Returning to the four outer nerves arising from the anterior 

 ganglia, it is found that in running backward they approach one 

 another slightly and that each passes through the dorsal or ventral 

 cephalic commissure , from which a few nerve fibres are received. 

 Behind the cephalic commissure they run nearly parallel with one 

 another, becoming the dextro-dorsal, sinistro-dorsal, dextro-ventral 

 and sinistro-ventral longitudinal nerves (PI. 21, Figs. 1, 2, 4 and 5), 

 In the scolex these are simple, rather compact bundles of nerves, 

 without ganglionic or "binding" cells; but in passing backward 

 ganglionic cells begin to appear in the neck region. At first these 

 are few, but as older proglottides are reached the number increases. 

 These nerves correspond exactly in origin , position and the course 

 taken with those described by Niemiec (1885) in Taenia coenurus 

 and T. strata. Niemiec was unable to trace them beyond the neck 

 region, but I have found them in proglottides taken from all parts 

 of the worm, and always occupying the same relative position in the 

 proglottis. Although I have not traced them continuously from pro- 

 glottis to proglottis through an entire strobila, I think that their occur- 

 rence in the same relative position in proglottides taken at random 

 in the same animal is evidence enough that they are continuous 

 throughout the entire length of the worm. 



2. In the Neck Region. 

 In the neck region of Monieza the most prominent nerves are 

 the six longitudinal ones. The two large lateral nerves arising from 

 the external horns of the cephalic ganglia lie in the usual position 

 external to the longitudinal excretory tube. They are single nerve 

 trunks nearly circular in cross-section, and not sharply defined in 

 outline. I have not succeeded in finding in Moniezia the two ac- 

 cessory lateral nerves which are described for other forms by Niemiec, 



