CHAPTER III. 



PHYLUM ECHINODERMATA* 



With a radial, usually pentamerous arrangement. The body- 

 wall contains calcareous plates and generally bears spines. The 

 coelom is divided into two well-marked portions the perivisceral 

 cavity and the watervascular system, and the gonads are not con- 

 nected with it in the adult. 



The Eehinodermata, like the Coelenterata, present a radial 

 arrangement of their principal organs and were for that reason 

 united by Cuvier with the polyps and medusae in the group 

 Radiata. With the progress of anatomical knowledge, it soon 

 became apparent that the organization of the Echinoderms 

 differs totally from that of the Coelenterates and belongs to a 

 much more complex grade of development. This fact, which 

 was first recognized by R. Leuckart, led to the separation of the 

 two groups and to the establishment of two independent phyla, 

 the Coelenterata and Eehinodermata. A trace of the old view 



* Fr. Tiedemann, Anatomic der Rohrenholothurie, des pommeranzfar- 

 benen Seesternes u. des Steinseeigels, Heidelberg, 1820. De Blainville, Manuel 

 d' Actinologie, Paris, 1834. L. Agassiz, Monogr. d'Echinodermes vivants 

 et fossiles, Neuchatel, 1838-42. L. Agassiz et E. Descr, " Catalogue raisonne 

 cles families, des genres et des especes de la classe des Echinodermes " 

 Ann. Sci. nat. (3), 6, 7, and 8, 1846-7. E. Forbes, A History of British 

 Starfishes, London, 1841. R. Leuckart, Ueb. d. Morphologic u. Verwandt- 

 schaftverhaltnisse d. wirbellosenthiere, Braunschweig, 1848. J. Miiller, 

 "Ueb. d. Bau d. Echinodermen," Abh. d. Berlin Akad., 1853. Id., " Sieben 

 Abh. iib. die Larven u.d. Entw. d. Echinodermen," Abh. d. Berlin Akad., 

 1846, 1848, 1849, 1850, 1851, 1852. A. Agassiz, " On the Embryology 01 

 Echinoderms." Memoirs of the American Academy, 1864. E. Metschnikoff, 

 " Studien iib. die Entwickelungsgesch. der Echinodermen u. Nemertinen," 

 St. Petersburg, 1869. H. Ludwig, " Morphologische Studien an Echino- 

 dermen," Z. f. w. Z., 1876-82. Id., " Echinodermen," in " Bronris Klassen 

 u. Ordnungen" in progress. O. Hamann, " Beitrage z. Histologie d. 

 Echinodermen," Jena. Zeitschrift., 1884-89. L. Cuenot, "Etudes 

 morphologiques sur les Echinodermes," Arch, de Biologie, 11, 1891. H. E. 

 Durham, " On Wandering Cells in Echinoderms, etc.," Q.J.M.S., 33, 1892. 

 P. H. Carpenter, several memoirs in the Q.J.M.S. and other Journals, 

 1875-1890. E. Ray Lankester, A Treatise on Zoology, Pt. 3, The Echino- 

 derma, London, 1900. E. \V. MacBride, Eehinodermata, in vol. I of the 

 Cambridge Natural History, 1906. 



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