46 PHYSIOLOGICAL SERIES. 



special branchial sense-organ (osphradium). The posterior 

 nerves are distributed to the mantle (particularly to the 

 papilhe that surround the inhalent opening) and to the 

 posterior adductor. 



In the lower specimen black paper has been placed 

 beneath the ganglia. 0. C. 130:'. I-://. 



AMPHINEUEA. 

 Plate, Zool. Jahrb., Suppl.-Bd. iv. 1898, p. 151. 



D. 44. The central nervous system of a Chiton (Ilanleya 

 alyssorum), showing some of its more important features. 

 The nervous system in this and other Amphineura consists' 

 fundamentally of two pairs of longitudinal cords united 

 anteriorly to a circumoral ring. An even layer of ganglion- 

 cells covers all parts of the cords and ring, without local 

 concentration to form special ganglia, except in the 

 Aplacophora and one species of Chiton. The outermost 

 pair of cords (lateral cords) lie in the body-walls above the 

 branchial furrow, lodged between the main branchial 

 renels; they innervate the mantle with its sense-organs, 

 and, from their slightly thickened posterior fourth, the 

 gills and probably also the renal organs and heart. They are 

 continuous with another above the rectum, and thus form an 

 elongated loop, comparable, apart from its relation to the 

 net um, to the visceral loop of Gastropods and Pelecypods. 

 The ventral or pedal cords extend throughout nearly tin- 

 whole length of the foot, buried in its substance. They 

 are united together by a large number of very delicate and 

 M.mewhat irregularly disposed commi ure-. and give oil' 

 from their outer and ventral surfaces numerous pedal nerves, 

 that unite to form a rich plexus in the muscles of the foot. 

 The lir-t and la-t of the series of peda'i commissures are far 

 -t outer than the rest, (in the specimen these two are 

 perfect, the roots only of the other commissures and of the 

 pedal nerves are shown). The pedal and lateral cords of 

 the same side unite together in front to form the band- 

 like anterior part of the circumoral ring. Behind the 

 mouth the ring is completed by a slender strand, that 

 terminates on either side in a swelling at the anterior end 



