HYDROIDA 



49 



there are in the colonies also numerous blastostyles, which are wholly devoid of rudiments of tentacles, 

 and accordingly only forming a stalk in the same way as is indicated by the diagnosis of Bonnevie. 

 But there always occurs a small polyp, and a "complete atrophy" of the polyp is in no case demon- 

 strable; nor is it obvious from the imperfect figure of Bonnevie (1899, Tab. I> Fig. 3). The great 

 variation of the blastostyles of the original specimens determined by Bergh, shows us that the 

 species stated by Bonnevie may be founded on a colony where the blastostyles carrying tentacles 

 were reduced to a minimum in number. But this does not give sufficient reason for maintaining it 

 as a peculiar species beside Hydractinia carica. 



Hydractinia carica is an Arctic literal species, which, in boreal waters, proves able to penetrate 

 along the West coast of Norway as far as Bergen (Text-fig. M). It has been found elsewhere only 

 in high arctic regions, in the Kara Sea, in the Murman Sea, and at Spitzbergen. It has also been re- 

 corded by Jaderholm (1909) from Davis Strait. 



Gen. Bougainvillia Lesson. 



Upright colonies with branched hydrocauli clothed with a perisarc. The polyps are fusi- 

 form with the tentacles placed in a whorl below the conically pointed oral portion. The polyps are 

 naked without the slightest attempt at formation of pseudohydrotheca round their proximal portion. 

 The gouophores are placed on the stems of polyps fully developed or reduced (blastostyles). In the 

 latter case, the unbranched polyp stem will sometimes rise from the hydrorhiza instead of from the 

 hydrocaulus. 



A closer inquiry into the distinguishing characters and their systematic value, shows us that there 

 is no reason to distribute the species of Bougainvillia on the three genera Bougainvillia, Dicoryne, and Hetero- 

 cordyle. Sufficient cause for distinguishing between Bougainvillia and the two other genera is not at all 

 given by the fact that the former has medusoid gonophores, while the two other genera have styloid go- 

 nophores. In mentioning the genera earlier treated, I have sufficiently explained the insignificance of this 

 criterion as to classification. Then remains the other distinguishing mark that the gonophores of Botigain- 

 villia develop on the stems of some fullgrown polyps, while in Dicoryne and Heterocordylc they are devel- 

 oped on the stems of reduced polyps (blastostyles). The genus Hydractinia shows us a full parallel to this 

 condition of things. But because of the many and close connecting links between one extreme and 

 the other, it has been agreed that the stronger and weaker specializing into nourishing polyps and 

 blastostyles cannot be employed as a generic character. When, on the other hand, this has been done 

 with Bougainvillia and Dicoryne and Heterocordyle, the only reason must be that, between the few 

 species known of these genera, most of the links occurring in Hydractinia are wanting. This lack, 

 in fact, is not a sufficient reason to elevate, in one case, the character to an importance which is denied 

 in another case, even within the same family. It is not right to base the genera Bougainvillia, Di- 

 coryne and Heterocordyle on characters that must be used with discretion as specific characters 

 in Hydractinia. Further, as to the distinguishing mark between Dicoryne and Heterocordyle, it is 

 still more diminutive. Heterocordyle conybcan All man, the only species known of the genus, is so like 



The Ingolf-Expedition. V. 6. 



