76 S. GOTO. 



describes a circle which is incomplete only at the hinder part. A 

 second nerve is given oif towards the hinder part of the sucker ; 

 this gives off at a short distance from its origin a small branch, and 

 after this, it takes a somewhat similar course in the hinder part to 

 that pursued by the first nerve in the anterior, but remains through- 

 out separate from its fellow of the opposite side. A third nerve is 

 given off towards the lateral part of the sucker ; but this soon 

 proceeds forwards, and runs almost concentrically with the first 

 nerve, but outside it near the margin of the sucker. This nerve 

 could be followed only for a comparatively short distance. These 

 three nerves all take their origin at the same point, and are repre- 

 sented in fig. 1, PI. XX. 



In Diclidophom (PI. X, fig. 5) and Monocotijle (PI. XVII, fig. 1), 

 the external lateral nerve could be traced along the ventro-lateral border 

 of the body almost up to the point of union with the internal lateral 

 nerve ; but in all the other genera that have come under my observa- 

 tion I could follow it only for a comparatively short distance ; and 

 in these it became gradually so small and its ti^isue so imperfectly dif- 

 fentiated from the surrounding mesenchyma that I could not be sure 

 whether I had the section of the nerve before me or not. The intei-nnl 

 lateral nerves, on the contrary, could always be distinctly followed up 

 to the region of the suckers ; and in Oiich-ocotijle, they become con- 

 tinuous with each other and form a loop at about the level of the 

 second pair of suckers, on the ventral side of the intestine (PI. XV, 

 fig. 2). 



In Tristomum, a pair of dorsal nerves has been described by some 

 writers, and I have myself observed it in Oncliocotijle ; but in all the 

 other genera, I could not demonstrate it with any satisfaction to 

 myself. 



The four posterior nerves are united with each other at regular 



