858 
MR. G. J. ROMANES AND PROFESSOR J. C. EWART 
trunk half-way up each ray, and the animal is then placed upon its back, the tetanic 
contraction of the muscles in the rays before mentioned as occurring under this form 
of section in detached rays, has the effect, when now occurring in all the rays, of 
elevating the disc from the floor of the tank. This opisthotonous-like spasm is not, 
however, permanent ; and the distal ends of the rays forming adhesions to the floor 
of the tank, the animal eventually rights itself, though much more slowly than 
unmutilated specimens. After it has righted itself, although it twists about the 
distal portions of the rays, it does not begin to crawl for a long time, and when it 
does so, it crawls in a slow and indeterminate manner. Star-fish so mutilated, how¬ 
ever, can ascend perpendicular surfaces. 
The loss of co-ordination between the rays caused by division of the nerve-ring in 
the disc is rendered most conspicuous in Brittle-stars, from the circumstance that in 
locomotion and in righting so much here depends upon co-ordinated muscular con¬ 
traction of the rays. Thus, for instance, when a Brittle-star has its nerve-ring severed 
between each ray, an interesting series of events follows. First, there is a long period 
of profound shock—spontaneity, and even irritability, being almost suspended, and the 
rays appearing to be rigid, as if in tetanic spasm. After a time, feeble spontaneity 
returns—the animal, however, not moving in any determinate direction. Irritability 
also returns, but only for the rays immediately irritated, stimulation of one ray causing 
active writhing movements in that ray, but not affecting, or only feebly affecting, the 
other rays. The animal, therefore, is quite unable to escape from the source of irrita¬ 
tion, the aimless movements of the rays now forming a very marked contrast to the 
instantaneous and vigorous leaping movements of escape which are manifested by 
unmutilated specimens. Moreover, unmutilated specimens will vigorously leap away, 
not only from stimulation of the rays, but also from that of the disc; but those with 
their nerve-ring cut make no attempts to escape, even from the most violent stimula¬ 
tion of the disc. In other words, the disc is entirely severed from all physiological 
connexion with the rays. 
If the nerve-ring be divided at two points, one on either side of a ray, that ray 
becomes ph} 7 siologically separated from the rest of the organism. If the two nerve- 
divisions are so placed as to include two adjacent rays—he., if one cut is on one side of a 
ray and the other on the further side of an adjacent ray—then these two rays remain 
in physiological continuity with one another, although they suffer physiological separa¬ 
tion from the other three. When a Brittle-star is completely divided into two portions, 
one portion having two arms and the other three, both portions begin actively to 
turn over on their backs, again upon their faces, again upon their backs, and so on 
alternately for an indefinite number of times. These movements arise from the rays, 
under the influence of stimulation caused by the section, seeking to perform their 
natural movements of leaping, which however end, on account of the weight of the 
other rays being absent, in turning themselves over. An entire Brittle-star when 
placed on its back after division of its nerve-ring is not able to right itself, owing to 
