6 THE POLYZOA RECOGNISED AS A DISTINCT GROUP. 



with scientific men, Thompson was quite unaware, when he pubhshed the result of his 

 researches, that Grant and Edwards had been before him in the field; his observations are, 

 therefore, original and independent, and, as he tells us they were made in the summer of 1820, 

 it would seem that it was only the delay of publication that has deprived him of the honour 

 of being the first to record a discovery so important in the history of zoology. 



In 1834 Ehrenberg published his 'Memoir on the Corals of the Red Sea.'* In this 

 work he proposed a new classification of the so-called polypes, dividing the entire group into 

 two great sections — the Antliozoa and the Bryozoa ; the former embraced the true radiate forms, 

 the latter corresponded to the Polyzoa of Thompson. Though the term Bryozoa had already been 

 used by him in a number of the ' Symbolse Physicre,' published in June, 1831, the priority of 

 publication is still left with Thompson's name, and though Ehrenberg's term is in general use 

 upon the Continent, and is largely adopted even by English writers, simple justice and the 

 laws of natural-history nomenclature demand the adoption of the term Polyzoa, and it is it, 

 therefore, which I have employed in the present Memoir. f 



Notwithstanding, however, the completeness with which the ascidian type of structure 

 had now been recognised in the Polyzoa, naturalists had not yet emancipated themselves from 

 the old notion that the closest aflanities of these animals were still with the Polypes, and the 

 Polyzoa, therefore, long continued to be classed with the Polypes, of which they M'ere still 

 considered as a group, though with distinct peculiarities, through which the Polypes manifested 

 an affinity with the Tunicata. 



It is not easy to say to whom we are indebted for the first absolute withdrawal of tne 

 Polyzoa from the Radiate sub-kingdom, and their location among the Mollusca. The obvious 

 justice of the step must have simultaneously presented itself to every naturalist who had made 

 the matter a special subject of study, while the important division of the Molluscan sub- 

 kingdom by Milne Edwards into the two primary sections of the MoUusca and the Molluscoida, 

 the latter including the Tunicata and the Polyzoa, leaves nothing now to be desired in the 

 systematic location of the Pol3'zoa. 



In the history of progressive discovery which has thus been sketched, eight distinct 

 epochs must be noted, each characterised by some one step which has more or less directly 

 led to the views at present entertained of the true afiinities and systematic position of the 

 Polyzoa. 1. The assertion by Imperato of the aniwality of coral. 2. The discovery by 

 Marsigliof the7Vo/j//;(?5 of coral, which he mistook for its flowers. 3. The determination of the 

 true nature of these polypes by Peysonelle. 4. The discovery of the Hydra by Leuwenhoeck. 

 5. The discovery of the "Polype a Panache,'^ and the determination of its structure by Trembley 

 and Baker. 6. The determination of the structure of certain marine Polyzoa by the 

 independent and nearly simultaneous labours of Grant, Edwards, and Thompson ; and the 

 recognition of the aSinity of these productions with the compound Ascidians by Edwards and 

 Thompson. 7. The designation, by a common independent name, of these animals by 

 Thompson. 8. The entire withdrawal of the Polyzoa from the Radiata and their association 

 with the iVloUusca. 



* 'Beitrage zur physiologischen kenntniss der Corallen-thiere im algemeinen, uud besonders des 

 Eothen Meeres.' 



f See an admirable criticism by Busk on tlie Priority of tlie terra Polyzoa, in tlie 'Annals of 

 Nat. Hist.,' vol. X, 1852. 



