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. Prom what 
I have observed, however, I am inclined to think that the proximate vertebrae 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, though 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, 
separated 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 with 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 caecal appendage. It would require, however, careful and 
special investigation of the subject to decide these questions with accuracy. 
DESCRIPTION OP THE PLATES. 
Tab. XIII. 
Solaster papposa. 
Fig. 1. Transverse or vertical section of ambulacral arch, a a. vertebral plates, resting against each 
other at the fulcrum (a x), upon which they move. b. water-canal for the supply of vesicles (i i) 
and feet (k Jc) : it rests upon the adductor muscle or inferior ligament which stretches between 
the tubercles («' a') of opposite plates, c. triangular recess between upper extremities of verte- 
or superior ligament, d. lower end of the ver- 
muscle 
(//) 
g. 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 a) from inferior muscle, found imbedded amongst delicate riband-like 
fibres (b b). 
Diagr 
modifi 
bb 
