IIYDROI1) ZOOPHYTES. 7 



SUB-FAMILY EUDENDRIINAE. 

 EtJDENDRIUM INSIGNE. 



(Plate L, fig. 4.) 

 insigne, Hincks, British Ilydroid Zoophytes (18G8), pp. 86-87. 



Localities. McMurdo Bay, February 20th and 28th, 1902; March 21st, 1903; 

 10-20 fathoms. 



This delicate little hydroid, consisting of small irregularly branched colonies, was 

 found attached to other Coelenterata, such as Ceratoisis and Campanularia. It did not 

 occur in great abundance, but a few colonies were found in several bottles of specimens 

 obtained in McMurdo Bay. 



Hydrosome. The hydrorhiza consists of a plexus of branching roots loosely 

 attached to its support. At frequent intervals it gives off hydrocauli, which 

 are themselves branched. These stems are very slender, strictly monosiphonic, 

 seldom upright, but growing in a straggling tangle like the stems of a climbing 

 plant searching for a new support. The hydrorhiza and the free hydrocauli are 

 invested by a thin straw-coloured perisarc, which is slightly annulated at the base of 

 and at intervals on the hydrocauli. 



There is considerable difficulty in distinguishing between hydrorhiza and the 

 stem, and many of the stems that are now free may possibly have been at one time 

 attached to the support. This difficulty renders the estimation of the height of the 

 colony a matter of conjecture, but it is about 25 mm. 



The perisarc frequently ends very abruptly at the base of the hydranths, 

 but in some cases it seems to attenuate gradually. 



The hydranths are ' 5 mm. in height and have the usual characters of the 

 genus. There are about twenty filiform tentacles 5 mm. in length, arranged in 

 a single verticel at the base of a trumpet-shaped hypostonie (fig. 4). 



At the base of the hydranth there is a circular groove bounded proximally 

 by a collar of very conspicuous deeply-staining cells (fig. 4, c.). Occasionally 

 both collar and groove are apparently absent. 



Hiucks does not give a clear figure of this groove or collar in the British 

 specimens, but states (p. 87) that " there is a circular groove near the base of the 

 body, from which the gouophores spring a portion of the structure which I 

 misinterpreted at first, and which led me to suppose that there was a shallow 

 cup round the base of the polypite." From this quotation it would appear that in 

 Hiucks' specimens, as in the Antarctic forms, the lower margin of the groove was 

 sometimes slightly swollen out to form a collar. In general form and size the 

 Antarctic specimens resemble the European specimens, but they differ from them 

 in the respect that the perisarc is less " closely ringed throughout." 



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