188 P. HERBERT CARPENTER, 
to the ambulacral nerves of the Crinoids and of the other 
Echinoderms, consisting as they do of longitudinal fibres 
and minute intercalated cells. This resemblance is so con- 
siderable that Baudelot (1) was only prevented from describ- 
ing these axial cords as the nerves of the Crinoids (as 
Dr. Carpenter had previously done (2) though unknown to 
him) by the fact of their occupying a dorsal and not a ven- 
tral position. Experiment shows that all the movements of 
the arms are dependent upon the integrity of their axial 
cords, and upon the connection of these cords with the cen- 
tral fibrillar envelope of the chambered organ, but that they 
are entirely unaffected by section of the ambulacral nerve 
(2, 3, 4). Removal of the chambered organ immediately 
stops the swimming movements of all the arms; they 
become rigidly straightened out by the action of their dorsal 
elastic ligaments, which the muscles are powerless to anta- 
gonise. But irritation of the chambered organ by a needle 
passed down the central funnel of the calyx of an eviscerated 
specimen causes all the arms to be suddenly and simul- 
taneously closed over the calyx. 
On the other hand, this last experiment shows that the 
movements of the skeleton are entirely independent of the 
oral nervous ring. This is contained in the visceral mass 
which is very readily removed from the calyx, but the swim- 
ming movements are altogether unaffected by this operation. 
They are performed as perfectly by the eviscerated calyx 
with its attached arms as by the entire and uninjured 
animal. 
Further, in many Actinometre, more or fewer, sometimes 
more than half the arms are unprovided with an ambulacral 
nerve (6, 8,9). Some of the ambulacral grooves radiating 
outwards from the peristome become slowly obliterated by 
the gradual, or occasionally sudden, approximation and 
union of their sides. Their ciliated epithelium with the 
subjacent nerve and blood-vessel become completely lost, 
and at the same time the water-vessel becomes very much 
reduced in size, and ceases to be connected with any lateral 
tentacular apparatus (Pl. XII, fig. 12, w.). Nevertheless, 
these ungrooved and nerveless arms take the same part in the 
swimming movements as those in which the ambulacra are 
entirely normal. They are usually those which are borne 
on the radii behind the mouth; but in some Actinometre, 
with two hundred or more arms, there are ungrooved arms 
upon each radius (9). 
The ambulacral nervous system, therefore, has no relation 
whatever to these movements. This is not to be wondered 
