ON THE LOCOMOTOR SYSTEM OF ECHINODERMATA. 
857 
The above observations have reference to the common Star-fish, but they apply 
equally to other Star-fishes, except that in Astropecten single detached rays are not 
able to right themselves when inverted (owing to the feet not being used by this 
species for this purpose, and to the other rays being absent), and that after division of 
the nerve in a ray of this species, the feet of the proximal portion usually manifest 
more activity than those of the distal. The destruction, however, of physiological 
continuity between the two portions is as complete as in the case of the common 
Star-fish. Single detached rays of Brittle-stars are able when inverted to right them¬ 
selves ; they wriggle round by means of their snake-like movements, and do not 
require, as is the case with the less active rays of Astropecten, the assistance of 
adjacent rays to effect the manoeuvre. On the whole, then, it may be said, as a 
general statement, that in all the species of Star-fish which we have observed, the 
effect of a transverse section of the nerve in a ray is that of completely destroying 
physiological continuity between the pedicels on either side of the section. 
The only other experiments in nerve-section to which the simple anatomy of a 
Star-fish exposes itself is that of dividing the nerve-ring in the disc ; or, which is 
virtually the same thing, while leaving this intact, dividing all the nerves where they 
pass from it into the rays. In specimens mutilated by severing the nerves at the 
base of each of the five rays, or by dividing the nerve-ring between each ray, the 
animal loses all power of co-ordination among its rays. When a common Star-fish is 
so mutilated it does not crawl in the same determinate manner as an unmutilated 
animal, but, if it moves at all, it moves slowly and in various directions. When 
inverted, the power of effecting the righting manoeuvre is seen to be gravely impaired, 
although eventually it is always accomplished. There is a marked tendency, as 
compared with unmutilated specimens, to a promiscuous distribution of spirals and 
doublings, so that instead of a definite plan of the manoeuvre being formed from the 
first, as is usually the case with unmutilated specimens, such a plan is never formed 
at all; among the five rays there is a continual change of unco-ordinated movements, 
so that the righting seems to be eventually effected by a mere accidental prepotency 
of some of the righting movements over others. Appended is a sketch of such unco¬ 
ordinated movement, taken from a specimen which for more than an hour had been 
twisting its rays in various directions (Plate 84, fig. 28). Another sketch is appended 
to show a form of bending which specimens mutilated as described are very apt to 
manifest, especially just after the operation. When placed upon their dorsal surface 
they turn up all their rays with a peculiar and exactly similar curve in each, which 
gives to the animal a somewhat tulip-like form (Plate 84, fig. 29). This form is never 
assumed by unmutilated specimens, and in mutilated ones, although it may last for 
a long time, it is never permanent. In detached rays this peculiar curve is also 
frequently exhibited; but if the nerve of such a ray is divided at any point in its 
length, the curve is restricted to the distal portion of the ray; it stops abruptly at the 
line of nerve-section. When entire Star-fish are mutilated by a section of each nerve- 
MDCCCLXXXI. 5 S 
