[18] Desc. Man, vol. ii., p. 134.
[19] Leidy. Rhizopoda of N. America, p. 16.
[20] Haeckel. Die Radiolarien, Berlin, 1862.
[21] Sollas. Spongidæ. Cassell's Nat. Hist. Vol. vi., p. 318.
[22] Allman's Hydroids. Ray. Soc., p. 123.
[23] Compare with Hydra above.
[24] Allman. Monograph of Tubularian Hydroida. Ray. Soc., p. 135.
[25] Allman, op. cit., p. 139.
[26] Huxley. Oceanic Hydrozoa, pp. 32, 46, 50.
[27] Fauna und Flora des Golfes von Neapel. Die Actinien. 1884.