1. Hyman, L. H., The Invertebrates: Echinodermata, 100 (McGraw-Hill, New York, 1955).
2. Breimer, A., Proc. K. ned. Akad. Wet., B 72, 139 (1969).
3. Peres, J. M., Bull. Inst. Océanogr. Monaco, 56, 1 (1959).
4. Magnus, D. B. E., Natur Mus., 93, 355 (1963).
5. Fell, H. B., in Physiology of Echinodermata (edit. by Boolootian, R. A.), 49 (Interscience, New York, 1966).