THE STRUCTURE OP XENIA HICKSONI. 229 



1834. Wilson, E. B.— " The Mesenterial Filaments of the Alcyonaria," 

 ' Mitt. Zool. Stat. Neapel,' v., 1884. 



1887. Haacke,W. — " Zur Physiologie der Anthozoen," ' Zoologischer Garten,' 

 Jahrg. xxvii., p. 284, 1887. 



1889. Weight, E. P., and Studer, T. H. — 'Challenger Reports,' Zoology 

 vol. xxxi., "Alcyonaria," 1889. 



1895. Bourne, G-. C. — " On the Structure and Affinities of Heliopora coerulea, 

 Pallas, with some Observations on the Structure of Xenia and 

 Heteroxenia," 'Phil. Trans.,' 1895. 



1895. Hickson S. J. — " The Anatomy of Alcyonium digiiatum," 'Quart. Jour. 



Micr. Sci.,' vol. xxxvii., part 4, 1895. 



1896. Schenk, A. — ' Olavulariiden, Xeniiden, und Alcyoniiden von Ternate,' 



Frankfurt-a.-M., 1896. 



1898. Ashworth, J. H.— "The Stomodeeuin, Mesenterial Filaments, and 

 Endoderm of Xenia," ' Proc. Roy. Soc.,' vol. lxiii., 1898. 



EXPLANATION OF PLATES XVIII.— XXII. 



Illustrating Dr. J. H. Ash worth's paper on " The Structure of Xenia Hicksoni, 

 nov. sp. with some Observations on Heteroxenia Elizabethce, Kolliker." 



List of Reference Letters. 

 A, A3, A5. Autozooids of Heteroxenia (the numbers refer to the table on p. 

 218). Cg. Coagulum in central cavity of sperm sac. Cn.O. Cnidoblast cell. 

 D.M. Dorsal mesentery. D.M.F. Dorsal mesenterial filament. Ect. Ectoderm. 

 Ect. Ch. Chain or cylinder of ectoderm cells round cylinder of denser mesogloaa. 

 Ect. Str. Strands of ectoderm cells. End. Endoderm. End. Can. Endodermic 

 canals. F. Flagella of siphonoglyph. G.C. Gland-cells in stomodseum. G.F. 

 Giant flagella of endoderm cells. Gen. 0. Genital cells in various stages of 

 development. Long. Can. Longitudinal endodermic canals. L.M. Lateral 

 mesentery. M. Mesentery. Mg. Mesogloea. Mg.D. Denser cylinder of 

 mosogloea around each coelenteron in stem. Mo. Mouth. Muc.G. Mucus cells 

 of ectoderm. M.P. Muscle processes of endoderm cells. N. Nucleus. Nem. 

 Nematocysts. N.C. Nerve Cells. N.F. Nerve fibrils. R.M. Retractor muscles 

 in mesenteries. S. S7. Siphonozooids of Heteroxenia (the number refers to the 

 table on p. 218). Sec. Secretion of gland-cells of stomodseum. Si. Siphono- 

 glyph. Sp. Spicules. Spz. Spermatozoa. St. Stomodteum. Sup. Can. Super- 

 ficial canal. S. S. Sperm sacs. V.M. Ventral mesentery. Z. Zooxanthellse. 



Plate XVIII. 



Fig. 1. — View of the colony of Xenia Hicksoni. From one of the stems 

 on the left side all the larger polyps have been removed, so that the umbellate 

 summit of the stem, with the young polyps growing round its edge, may be 



