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 E. Hertwig ^ " Zunachst ist fiir mich die schon oben vertheidigte Grund- 

 anschauting maasgebend dass die Lcbenserscheinungen der Ctenophoren nicht gut ohne 

 die Annahme eines mesodermalen Nervensystems verstandlich sein mochten. Seitdem 

 durch die neueren Untersuchuugen mit sicherheit Nerven bei den Medusen und Actinien 

 nachgewiesen worden sind, ist kein Fall im Thierreich bekannt, in welchem complicirtere 

 und raschere Muskelbeweguns-en ohne sleichzeitige Anwesenheit von Nerven zu Stiinde 

 kamen. Soil ten die Ctenophoren in dieser Hinsicht eine Ausnahme machen ?" 



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 tbe 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 (PI. XXIV. figs. 1-5, ca.), 

 and also in the ventral perisome, whether bare or plated (PI. LIX. figs. 2-4, 6, 7; 



' Ueber deu Ban der Ctenophoren, Jenaisclie Zeitschi:, Bd, xiv. p. 437. 

 2 Proc. Boy. Soc. Loud., 1876, p. 453. 



