DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID^. 119 



The ganglion and interambulacral nerve-cords are well-developed. The relation they 

 bear to the skeleton will at once be understood by referring to fig, 8, Plate XII. The 

 perioral spines are only four in number ; and the masses {b b) bearing them support also 

 the vertebral plates [a a) directly, there being no intermediate piece. The integument is 

 firmly connected to the fibrous tissue beneath, as far outwards as the interambulacral 

 cords. These latter have a close relation to the vascular perioral ring connected to the 

 heart. 



Microscopically, " the ganglions are a collection of nerve-cells clustered together and 

 forming a union, as it were, between the interganglionic and ambulacral nerve-cords*. 

 Filaments pass outwards, and also to the different cords in connexion with it. Some may 

 likewise be detected passing inwards to the perioral space." Other " small filaments 

 diverge outwards, very soon passing backwards into the interior of the animal, through 

 small foramina in the calcareous plates." t 



The interambulacral nerve-cords have each " a series of cells arranged pretty nearly in 

 a line, and sending filaments longitudinally as well as inwards and outwards." 



On the JRej^rodnctioii of lost Mays. 



Before concluding, I would offer, though still imperfect, some few observations, made 

 at different times, upon the reproduction of the lost rays in Uraster rubens. The speci- 

 mens I examined were gathered close to Newhaven Pier, and were therefore principally 

 those which had survived the rough handling and ill-treatment of the fishermen. They 

 can be procured of all shapes, from four- to one-rayed, and with the reproduced portions 

 in all stages of development. These stages I have attempted to give in a series of five 

 drawings $. 



After a ray has been torn off or otherwise destroyed, the healing process commences 

 by the disintegration and subsequent rejection of those portions of the integument and 

 skeleton which have undergone fatal laceration. While this is going on, the dorsal skin 

 with its calcareous network curves downwards and slightly inwards upon itself, until it 

 reaches the vertebral arch. Union then begins in the mesial line by the dorsal flap send- 

 ing inwards a small pointed process, which becomes connected to the integument and the 

 fibrous tissue of the vertebral arch. The lateral portions of the flap next cicatrize, with 

 the skin covering the ambulacral aspect of the vertebral plates. Their broad siu'faces, 

 however, remain free, — a distinct cul-de-sac existing between them and the dorsal integu- 

 ment, very well seen in a longitudinal section. 



A prolongation from the ambulacral nerve-cord is soon observed, covered, of coiu-se, by 

 the skin, and supported on its dorsum by a soft tubercle which is developed simultaneously 

 with it from the dorsal flap. This is followed by the deposit of pigment ; but whether 

 it is a perfect eye at this stage, I am stUl uncertain. It soon, however, presents the cha- 

 racteristic cones, each with the small clear spot at its base. The subsequent stages are 

 the further elongation of the cord and of the dorsal integument, with the development of 

 the vertebral plates and suckers. 



* Plate XV. fig. 7. t Thesis. % Plate XV. figs. 10-14. 



