120 DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID.E. 



Whether the prolongation of the axis of the ray be effected by the formation of verte- 

 bral plates at the proximal or the distal portion, remains still to be decided. Erom what 

 I have observed, however, I am inclined to think that the proximate vertebrte are the older. 

 It is a curious fact, that, although the skeleton of the new ray appears very soon after 

 this begins to be reproduced, yet no calcareous deposit takes place, in the fibrous structure 

 connecting it to the remnant of the old ray, for a very long time. Probably this fibrous 

 structure is the result of the cicatrix ; and most likely, before any calcification begins, it 

 is entirely absorbed and new tissue developed. 



The integument of the young ray remains for a long time quite colourless ; so that, on the 

 dorsum of the animal, especially if it have much pigment, the line of demarcation between 

 the old and the new skin is very distinct. 



The question now naturally arises, as to how far a Starfish may be mutilated and still 

 retain life, and, therefore, the power of reproducing its lost parts ? Amongst the great 

 number I have examined, none have had all the rays destroyed at once, thoixgh many 

 have had all but one. None of the rays which reproduced another had the whole of the 

 ambulacral cord destroyed ; and none had the stomach injured. Although many rays, 

 sejaarated from the Starfish, are found moving about briskly, and apparently quite lively, 

 nevertheless this apparent life does not continue long, the dorsal skeleton becoming first 

 disintegrated (the suckers still remaining moveable and contractile), and lastly the ver- 

 tebrae wdth the feet, &c. Evidently more circumstances than one are essential for the 

 prolongation of the animal's life, the chief of which seem to be, an uninjured stomach, 

 with, at least, one entire csecal appendage. It would requii'e, hoM^ever, careful and 

 special investigation of the subject to decide these questions with accuracy. 



DESCRIPTION OE THE PLATES. 

 Tab. XIII. 



Solaster jicipposa. 



Fig. 1. Transverse or vertical section of ambulacral arch, a a. vertebral plates, resting against each 

 other at the fulcrum (« x), upon which they move. b. water-canal for the supply of vesicles {i i) 

 and feet [kk) : it rests upon the adductor muscle or inferior ligament which stretches between 

 the tubercles [a' a') of opposite plates, c. triangular recess between upper extremities of verte- 

 bral plates, filled up by the abductor muscle or superior ligament, d. lower end of the ver- 

 tebral plate : it rests upon a rounded calcareous mass (e) bearing a number of spines (//). 

 ff. ambulacral nerve-cord, consisting of nerve-cells whose filaments may be traced passing 

 through the substance and by the side of the inferior muscle, and extending upwards round the 

 water-vessel, h. integumentary covering. 



Fig. 2. Fusiform nucleated cells (« a) from inferior muscle, found imbedded amongst delicate riband-like 

 fibres [b b). 



Fig. 3. Diagrammatic view of perioral skeleton, a a. modified vertebral plates, the first of the series, bb 



