HISTORY OF RESEARCH. 17 



it by uniting witli tlic mcdusoid form wliicli constitutes the Gymnophthnlmin of Forbes, not only 

 the polypoid forms of liydroids, but also the Siphonophora. The Gi/mnopJilludmia of iM'Crady 

 thus correspond to the lljdromedusida and lljjdroidea of KoUiker united. 



In a small treatise on the alternation of generations among the liydroids,' Gegenbaur had 

 already contributed some valuable observations to our knowledge of the generative phenomena 

 and life-history of the IIydkoida; while, as we have seen, he had also made the so-called naked- 

 eyed ]\Iedusa3 a subject of careful systematic study. In his ' Outlines of Comparative Anatomy,' 

 pubhshed in 1859,^ he retains his divisions of Acraapeda and Craspedota, uniting them into 

 a single order, Medusida, while he combines the various non-natatory hydroid colonies into 

 another order under the name of Ilydroidu. 



In 1859 Huxley gave us a monographic treatise on the Siphonophora observed during the 

 circumnavigatory voyage of H.M.S. "Rattlesnake."' The "Rattlesnake" was fitted out in 

 1 846, imder the command of Captain Owen Stanley, for the purpose of surveying the channel lying 

 within the great barrier reef which extends along the east coast of Australia, and for the explora- 

 tion of the neighbouring seas ; and the expedition was accompanied by Mr. Huxley as assistant- 

 sm-geon. Owing to the refusal of the Admiralty, on the return of the expedition, to furnish the 

 means of publication, the results of Huxley's observations remained unpublished, until, after many 

 fruitless attempts to obtain the aid of Government, and many years of vexatious delay, the 

 Ray Society undertook the task of publication. In this valuable work the Siphonophora are 

 described under the designation of Oceanic Ilydrozoa. The special part of the treatise is preceded 

 by a general introduction, which abounds in original and philosophic views of the morphology of 

 the Hydroida and of their relation to the other groups oi Hydrozoa ; and the author proposes 

 a new and comprehensive terminology, much of which has been adopted in the present 

 Monograph. In his systematic arrangement of the Hydrozoa; he does not venture to unite 

 into a single group with the polypoid phases of the Hydroida those hydroid Medusae which 

 have not been proved to proceed from a polypoid trophosome, but prefers to arrange them 

 as a distinct order of Hydrozoa under the name of Medusidee, attaching, however, only a 

 provisional significance to the group thus constituted. 



Between 1860 and 1862 there appeared the third and fourth volumes of Agassiz's 'Con- 

 tributions to the Natural History of the United States.'* These volumes are devoted to the 

 Hydrozoa, which are treated of under the designation of Acalepha?. We learn from the 

 preface to the first volume that the author has been assisted by Prof. H. J. Clark, to whom 

 the microscopical researches which form so valuable a portion of the work are mainly due. 

 Many new genera and species of liydroids are described, and their tropliosomes as well as 

 gonosomes represented in elaborate and beautiful figures drawn from the living animal, while 

 the number and beauty of the drawings expressing anatomical and embryological details give to 



^ Carl Gegenbaur, ' Zur Lelire voni Generationswechsel uud dor Fortpflauziing bei Medusen nud 

 Polypen,' Wurzburg, 1854.. 



" Carl Gegenbaui', ' Grundziige der Yergleichenden Auatomie,' Leipzig, 1839. 



^ Thomas Henry Huxley, 'The Oceanic Hydrozoa; a Description of the Calycoplioridae and Phy- 

 sophoridK observed during the Voyage of H. M. S. " Rattlesnake," in the years 184G-50.' London, 

 printed for the Ray Society, IS.'iO. 



* Louis Agassiz, ' Contributions to the Natural History of the United States of America,' 

 Boston, 1857—62. 



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