. Comparative anatomy and physiology. Chap, xii.] NERVOUS SYSTEM OF CRINOIDS. 409 the nerve in the arm of a starfish, and it has similar relations to a nerve ring which runs round the mouth. If we now look at the opposite side of the section, we find another and larger cord which gives oft branches to the muscles of the arms (a a'} ; this cord, if it be followed up, will be found to end in an organ, the so - called " chambered organ," which lies in the centred orsal piece (see page 292) of the Crinoid. Now, if the visceral mass, part of which is the circumoral nerve ring, be alone re
. Comparative anatomy and physiology. Chap, xii.] NERVOUS SYSTEM OF CRINOIDS. 409 the nerve in the arm of a starfish, and it has similar relations to a nerve ring which runs round the mouth. If we now look at the opposite side of the section, we find another and larger cord which gives oft branches to the muscles of the arms (a a'} ; this cord, if it be followed up, will be found to end in an organ, the so - called " chambered organ," which lies in the centred orsal piece (see page 292) of the Crinoid. Now, if the visceral mass, part of which is the circumoral nerve ring, be alone removed, the arms will continue to move as regularly as they did before, and the Crinoid will still be able to about in the If, 011 the other the five - cham- >rgan be stimu- then, as Dr. has shown, sudden and swim water hand, bered lated, Carpenter there is a. CL simultaneous all the flexion of arms. The ex- Fig. 177.—Cross Section of a Pin- nule of the Arctic Featber- star (Antedon eschnchti]; x 75. a, Axial cord ; a', its branches ; ag, ambu- lacra! groove; b, radial blood- vessel ; gv, genital vessel ; ov, ovary ; n, radial nerve ; pj, pinnule joint; w, water-vessel; T, tentacle. (From Carpenter, altered from Ludwig.) istence of these two apparently independent nerve systems in a Crinoid is a difficulty which the morphologist has not yet been able to solve, but the anatomical and physio- evidence in favour of the nervous nature logical. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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