114 THE VOYAGE OF H.M.S. CHALLENGER. 
Some species have as many as two hundred arms, each consisting of from 
one hundred and twenty to two hundred joints; while I have counted three 
hundred joints in the arms of a large Antedon eschrichti. The regular and 
graceful mode in which a ten-armed Crinoid swims is well known. The simul- 
taneous flexions of the five right and of the five left arms alternately involve the 
co-ordinated contraction of several hundred pairs of well defined muscular bundles, and 
yet these are performed in entire independence of the ambulacral nervous system, with 
which the muscles are in no direct connection. In fact the eviscerated skeleton which 
has lost its disk and oral nerve-ring will swim as well as the entire animal. Whence 
does it get this power ? 
According to R. Hertwig * “ Zuniichst ist fiir mich die schon oben vertheidigte Grund- 
anschauung maasgebend dass die Lebenserscheinungen der Ctenophoren nicht gut ohne 
die Annahme eines mesodermalen Nervensystems verstiindlich sein michten. Seitdem 
durch die neueren Untersuchungen mit sicherheit Nerven bei den Medusen und Actinien 
nachgewiesen worden sind, ist kein Fall im Thierreich bekannt, in welehem complicirtere 
und raschere Muskelbewegungen ohne gleichzeitige Anwesenheit von Nerven zu Stiinde 
kamen. Sollten die Ctenophoren in dieser Hinsicht eine Ausnahme machen 2” 
Substitute for “ Ctenophoren” the name “ Crinoideen” in the above quotation, and 
the question arises, Where is the co-ordinating centre of the muscular movements of a 
Crinoid ? 
A centre of this kind, if it exists in such a highly organised type as a Crinoid, cannot 
but be regarded as belonging to a nervous system; whereas a denial of its existence 
brings us face to face with a physiological problem of much complexity. As a matter 
of fact, however, there is both physiological and anatomical evidence for the existence of 
such a centre, though the morphological difficulties which its presence involves are of 
the most perplexing character. 
The well-known experiments of Dr. Carpenter? have shown conclusively that the 
fibrillar envelope of the chambered organ is the governing centre on which all the 
muscular movements of the animal depend, and that the movements of each individual 
arm depend upon the integrity of the axial cord of that arm. For they stop directly 
it is injured, just in the same way as injury to the chambered organ causes all the arms 
to be rigidly stretched out by the action of the dorsal elastic ligaments. The fibrillar 
envelope of the chambered organ, therefore, is the centre of a nervous system, the peri- 
pheral portion of which consists of the axial cords of the rays, arms, and pinnules, and of 
the numerous branches proceeding from these cords. 
The occurrence of this fibrillar tissue in the stem and cirri (Pl. XXIV. figs. 1-5, ca.), 
and also in the ventral perisome, whether bare or plated (Pl. LIX. figs. 2-4, 6, 7; 
1 Ueber den Baa der Ctenophoren, Jenaische Zeitschr., Bd, xiv. p. 437. 
2 Proc. Roy. Soc. Lond., 1876, p. 453. 
