344 HYDRACTINIA. 



to another genus, namely, Podocori/ne, sliortly afterwards instituted by Sars, and we have at 

 present no chie to enable us to say which of these two forms was intended. 



In the following year the Hydractinia of Van Benedcn became the subject of an elaborate 

 and beautifully illustrated memoir by j\I. de Quatrefages, in which this animal was described 

 under the name of Synhydra parasites} De Quatrefages here shows that the zooids which 

 support the gonophores are destitute of mouth, and are otherwise of a different fomi from the 

 alimentary zooids of the colony. It is true that Van Beneden, in the memoir just referred to, 

 has figured a gonophore-bearing zooid as deprived of tentacles, but he has made no allusion to it 

 in the text, while De Quatrefages has not only fully described it, but has insisted on its constancy 

 and its value as affording a character of generic importance. De Quatrefages must therefore be 

 fairly regarded as the first who has made us properly acquainted with the occurrence of a blasto- 

 style among the Tubularian hydroids, a form of heteromorphism of great importance in its bearing 

 on the morphology of this group of animals. 



De Quatrefages' memoir, notwithstanding some erroneous views, which could scarcely have 

 been avoided in the state of hydroid zoology when he wrote, contains by far the best account 

 which had up to that time been given of this interesting hydroid, and is perhaps the most valuable 

 which had appeared on any hydroid since the publication of Loven's famous memoir on Campanu- 

 laria and Syncorync.' The name of Synhydra, however, must yield to that of Hydractinia, 

 whose acceptance among zoologists has been secured by the fact of its prior publication. 



In 1844 Van Beneden defined for the first time his genus Hydractinia, under which he 

 included two species with the names of Hydractinia rosea and Hydractinia lacteal He has 

 since, however, admitted that these two forms are only different sexes of one and the same 

 species. Indeed, there is no reason for supposing that the animal on which Van Beneden 

 founded his genus Hydractinia is other than the Alcyonium echinatum of Fleming ; and notwith- 

 standing Fleming's entire misapprehension of the affinities of this animal, his specific name must 

 stand instead of either of those assigned to the hydroid by Van Beneden, a change to the justice 

 of which the distinguished Belgian naturalist himself assents in a subsequent memoir. 



In 1S5G an excellent account of Hydractinia ecldnata was published by Dr. Strethill 

 Wright.* His observations on its structure are very full and accurate, and his memoir supple- 

 ments in many important points what had hitherto been published on this hydroid. He calls 

 attention to the curious spiral zooids which occur near the margin of the colony, structures 

 with which I had myself become acquainted several years before, though Dr. Wright was the 

 first to publish an account of them. 



In 1862 Agassiz described under the name of Hydractinia polyclina a North American 

 representative of this genus, which differs very slightly from the European form. He makes it 

 the subject of one of the elaborate and finely illustrated memoirs in his great work on the 

 natural history of the United States.^ 



Finally, in 18GG, Van Beneden gives us a second and mere extended description, with new 



^ 'Ann. des Sc. Nat.,' 181-3, vol. xx. 



- ' Wiegnian's Arcliiv,' 1837. 



^ ' Reclierches sur les Tubulaiies.' 



* ' Edin. New Phil. Journ.,' April, 1857. 



» ' Contr. Nat. Hist. U.S.,' vol. iv, p. 227. 



