PENNATULIDA DREDGED BY H.M.S. "TRITON." 147 



and Virgularia, and Wilson ""' has recently shown that the same applies to the 

 sexually produced young of Renilla. It appears, therefore, that the unitenta- 

 cular condition of the Umbellula zooid is not a repetition of any stage occurring 

 in the ontogeny of the normal Pennatulid polyp. It is, however, just possible 

 that such a stage once existed in the phylogeny of the group, but has dropped 

 out of its ontogeny. So far as is known, a unitentacular condition does not 

 obtain in the ontogeny of any Alcyonarian, though we must bear in mind that 

 very few forms have as yet been studied adequately. Among Zoantharia a 

 temporary unitentacular condition occurs in Actinia mesembryantliem.um,\ while 

 in Cerianthus and Arachnitis four tentacles arise simultaneously, and in other 

 cases all eight. 



The definite relation of the single tentacle of the Umbellula zooid to the 

 plane of symmetry seems to indicate that it has some morphological signi- 

 ficance, though at present we have not evidence to determine what that 

 significance is. I would, in conclusion, direct attention to the remarkable 

 condition of the polyps in Scytalium tentaculatum, K6ll.,t one of the " Chal- 

 lenger " species, in which each polyp has but a single tentacle, as showing that 

 a unitentacular condition may be more widely spread than is at present 

 suspected. 



Our knowledge of the genus Umbellula has been very greatly increased of 

 late years. Two specimens taken off the coast of Greenland in 1752, and very 

 imperfectly described, were for more than a century the only examples recorded. 

 In 1871 Lindahl obtained two specimens, one in Baffin's Bay in 410 fathoms, 

 and the other at the entrance to the Omenakfjord, in N. Greenland, at a depth 

 of 122 fathoms. An Umbellula was also obtained by Nordenskiold in the 

 Kara Sea, to the east of Novaya Zemlya, during the " Yega " expedition. 



The " Challenger " expedition added enormously to our knowledge of this 

 genus, no less than seven new species being obtained from widely different 

 parts of the world. Concerning the geographical distribution of this genus 

 Kolliker says: — "After having known for more than a century only one 

 locality, the North Polar Sea, near the coast of Greenland, we have now learned 

 that this form is far and widely distributed. Umbellula' have now been 

 obtained from the North Atlantic Ocean (between Portugal and Madeira); 

 from the North Polar Sea, coast of Greenland; from the Atlantic Ocean, under 

 the Equator, between Africa and America, and from the west coast of Africa, 

 north of Sierra Leone (Stud.) ; from the South African Sea, west of Kerguelen 

 Island ; from the South Polar Sea ; from the coasts of New Guinea and of 



* Wilson, " The Development of Renilla," Proc. Roy. Soc, 1882. 



f -Lacaze-Duthiers, " Developpement des Coralliaires," Archives de Zoologie experimentale et 

 generale, vol. i. 1872, and vol. ii. 1873. 



% Kolliker, Zool. Chall. Exp., part ii., 1880, pp. 10, 11, and pi. iii. fig. 12, pi. iv. fig. 13. 



