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XI. The Nervous System of the Asteridae ; with observations on the Structure of then 
Organs of Sense, and remarks on the Reproduction of lost Rays. By Henry S. 
Wilson, M.D., Junior Demonstrator of Anatomy in the University of Edinburgh. 
Communicated by Thomas Anderson, M.D., F.L.S. 
Read June 7th, 1860. 
COMPARATIVE anatomists have hitherto adhered very closely to Tiedemann's de- 
scription of the nervous system of the Asteridae. Muller was the first to point out certain 
errors in his description, and to substitute for it a more perfect anatomical arrangement, 
although he did not enter into a minute detail of the nerve-centres. 
In the month of June 1858, I submitted to the Senatus Academicus of the University 
of Edinburgh, as my graduation thesis, "Observations on the Nervous System of 
Asterias," which I had made, from time to time, during the preceding year. Since that 
date I have investigated the subject anew, and considerably extended my observations. 
Dr. Haeckel, in Von Siebold und Kdlliker's ' Zeitschrift fur Wissenschaftliche Zoologie' 
ot December 1859, published some observations on the eye-spots of Astropecten aurantiacus, 
Asteracanthion glacialis, and Asteriscus verruculatus, in which he incorporated some 
remarks on the microscopic characters of the nerve-cords ending in these eye-spots. 
The 
ystem consists, in Asterias and other Echinodermata, of a perioral 
irom which, opposite each ambulacral groove, nerve-cords pass along the ventral surface 
of the 
ay 
Ihe ambulacral nerve-cords are, as stated by Muller, connected to each other by inter- 
ambulacral cords, — the latter forming, as a whole, a more or less perfect ring according 
to the number of rays the animal may possess. Thus, in the 5-rayed starfishes the ring 
becomes pentagonal, whilst in the 13-rayed, it is almost circular. The ambulacral cord 
Begins, in Asterias, with a ganglionic enlargement, which rests upon the first two or 
tnree of the long series of vertebrae forming the ambulacral groove. This ganglion con- 
sists of a cluster of nerve-cells, principally unipolar, whose filaments pass off obliquely 
rom either side along each interambulacral cord, and mesially along the ambulacral cord, 
ner nerve-fibres may occasionally be seen running diagonally across, to the space be- 
ween the rays, and then disappearing, probably to supply the viscera. The cord alon^ 
he ambulacral groove is simply a continuation in structure of the ganglion itself. It 
consists of unipolar nerve-cells, arranged along the mesial plane of the groove, and ly 
& 
immediately beneath the integument, between the two central rows of feet. Bipolar 
nerve-cells may occasionally be seen, though they are proportionately few. The fibres 
rom the cells pass, some longitudinally with the cord, others laterally to either side, 
probably to supply the suckers, while a third set run vertically upwards (supposing 
a e animal in its normal position, with the mouth downwards) through the inter- 
p2 
