94 



MEDUS.E OF THE WORLD. 



from the ectoderm of the subumbrella cavity of the bell. The medusa is hermaphroditic; ova 

 develop in the ventral, and sperm in the dorsal (aboral) wall of the brood-pouch. 



The hydroid is Clavatella of Hincks, 1861 (Annals and Mag. Nat. Hist., ser. 3, p. 73, 

 plates 7, 8; Ibid., 1868, British Hydroids, vol. I, p. 73, plate 12, fig. 2). In Clavatella the 

 polypites arise singly from a linear stolon. The polypites are small linear, or clavate, with 

 a zone of 8 slender tentacles which terminate each in a knob of nematocysts. The medusa-buds 

 are borne only on two opposite sides of the body of the polypite near its base. The hydroid 

 lives on Ulva in shallow tide pools, and the medusae are produced in summer and autumn. 



Hartlaub found that the entoderm of the planula of Eleuthe ria contains numerous nema- 

 tocyst-cells. Krumbach, 1907, believes that Tnchoplax, F. E. Schulze, 1891 (Abhandl. Akad. 

 Berlin), is the creeping planula of Eleuthena. 



Elfuthcna, Cladonema, and Amphogona are the only genera of hydromedusae known to 

 be hermaphroditic. 



Fit;. 46. Hydroid (Clavatella prolifera) and its medusa (Eleutheria dichotoma), after Allman, in Ray Society, 1871, 1872. 

 FIG. 47. Clavatella prolifera, after Hincks, in British Hydroid Zoophytes. 



Eleutheria dichotoma Quatrefages. 



Eleulheria dichotoma, QUATREFAGES, 1841, Compt. rend. Acad. Sci., Paris, tome 15, p. 1 68; 1842, Annales Sci.Nat., Ser. 2, p. 270, 



plate 18. KROHN, 1861, Archiv. Naturgesch., Jahrg. 27, p. 157. 

 Clavatella prolifera (hydroid), HINCKS, 1861, Annals and Mag. Nat. Hist., ser. 3, vol. 7, p. 73, plates 7, 8; 1868, Hist. British 



Hydroid Zoophytes, p. 73, plate 12, fig. 2. 



Non Eleutheria dichotoma, CLAPAREDE, 1863, Beob. Anat. und Enrwick. wirbelloser Thiere, p. 4, taf. i, fign. 4-10. 

 Clavatella prolifera (hydroid), ALLMAN, 1872, Monog. Tubul. Hydroids, pp. 31, 212, 384, plate 18. 

 Eleutheria dichotoma (non claparede), HAECKEL, 1879, Syst. der Medusen, p. 106. 

 Eleutheria dichotoma, GRAEFFE, 1884, Arbeit, Zool. Inst. Wien, Bd. 5, p. 353. HARTLAUB, 1886, Zool. Anzeiger, Bd. 9, p. 706, 



I fig. Also: Ibid., 1887, Bd. 10, p. 652; 1907, Nordisches Plankton, Nr. 12, p. 127, fign. 1 19, 120. BEDOT, 1905, Revue 



Suisse de Zool., tome 13, p. 133 (literature cited to 1850). MULLER, 1908, Zeit. fijr wissen. Zool., Bd. 89, pp. 34, 73, 



taf. 3, fign. 3-7 (origin and structure of eggs). 



This medusa is exceedingly variable, but the normal form may be briefly described as 

 follows : 



Bell irregularly hemispherical, with its lower surface more or less 6-sided. 0.3 to 0.4 mm. 

 wide. There is a ridge of large nettling warts extending around the margin. There are 6 ten- 

 tacles at the ends of the 6 short radial-canals, and not irregularly arranged in reference to the 

 radial-canals as in E. claparedii Hartlaub = E. dichotoma Claparede. 



