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XI. The Nervous System of the Asteridse ; with observations on the Structure of their 

 Organs of Sense, and remarks on the Reproduction of lost Bays. By Henet S. 

 Wilson, M.B., Junior Demonstrator of Anatomy in the University of Edinburgh. 

 Communicated by Thomas Andekson, M.B., 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 Asterldse. Mliller 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 Ediuburgh, 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 Kolliker's ' Zeitschrift fiir Wissenschaftliche Zoologle' 

 of December 1859, published some observations on the eye-spots of Astropecten au,rantiacus. 

 Aster acanthion glacialis, and Asteriscus verruculatus, in which he incorporated some 

 remarks on the microscopic characters of the nerve-cords ending in these eye-spots. 



The nervous system consists, in Asterias and other Echinodermata, of a perioral ring, 

 from which, opposite each ambulacral groove, nerve-cords pass along the ventral surface 

 of the ray. 



The ambulacral nerve-cords are, as stated by Mliller, 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 

 three of the long series of vertebra? forming the ambulacral groove. This ganglion con- 

 sists of a cluster of nerve-cells, principally unipolar, whose filaments pass oif obliquely 

 from either side along each interambulacral cord, and mesially along the ambulacral cord. 

 Other nerve-fibres may occasionally be seen running diagonally across, to the space be- 

 tween the rays, and then disappearing, probably to supply the viscera. The cord along 

 the ambulacral groove is simply a continuation in structure of the ganglion ItseK. It 

 consists of unipolar nerve-cells, arranged along the mesial plane of the groove, and lying 

 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 

 from the cells pass, some longitudinally Math the cord, others laterally to either side, 

 probably to supply the suckers, while a third set run vertically upwards (supposing 

 the animal in its normal position, with the mouth downwards) through the inter- 



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