ON TEMNOCEPHALA. 293 



of fibres. Finally, the longitudinal cords, much diminished in 

 size, unite together near the posterior border. 



The whole course of these dorsal cords and their branches 

 can be made out much more readily than in the case of the 

 others. If an alcoholic specimen of T. fasciata be macerated 

 for a day or two in weak bichromate of potash and weak 

 alcohol, and the cuticle, epidermis, and muscular layers, with 

 the outer layer of pigment carefully stripped off, the nerves 

 are readily traced by the light lines which they form among 

 the pigment of the nervous layer. In young specimens of the 

 same species in which the outer layer of pigment is imperfectly 

 developed, more or less of the course of this series of nerves 

 can usually be seen, and in the New Zealand T. novse- 

 zelandise in which the outer layer of pigment is little deve- 

 loped or absent, the nerves are readily traceable even in the 

 adult. In the case of the other sets of nerves resort must be 

 had in tracing them to the study of series of sections, and I 

 am not able to give more than a general account of their dis- 

 tribution. 



The second pair or dor so -lateral cords (PI. XXI, fig. 4, and 

 PI. XXI, fig. 12, d. I. n.) run backwards on the dorsal aspect 

 of the body immediately outside the testes, not far from the 

 lateral border. It is of larger size than the dorsal, and sends 

 off branches between the organs. The ventral cords (v. n.) 

 are the largest. From the ganglion they curve round the 

 pharynx and run along the ventral aspect in the angle between 

 the testes externally, and rather farther from the median line 

 than from the lateral border. The ventral and lateral longi- 

 tudinal cords are connected by transverse branches, and the 

 ventral cords of opposite sides are united similarly by numerous 

 transverse commissures. 



The nerve-fibres (PI. XXII, figs. 2 and 3) of which these 

 longitudinal cords and their branches consist, are large fibres 

 averaging '01 mm. in diameter, of very delicate material, which 

 is not readily acted on by staining agents, enclosed in a more 

 resisteut sheath. The central material shrinks greatly in pre- 

 served specimens, and this with its being little affected by dyes 



