HISTORY OF RESEARCH. 11 



structure of most of the animals constituting the Jladiatn of Cuvier was still so very imperfectly 

 known that this important character failed to receive its due weight in classification. 



In 1828 it was brought out with greater distinctness and force by M. Milne-Edwards in 

 an account of his zoological researches in the Chausey Isles' ; but still the fixed plantlike 

 hydroids continued to be associated with the true corals and PoJijzoa, under the common name 

 of " Polypi," for, notwithstanding the deep-lying difference which had been indicated by Cuvier, 

 and more definitely insisted on by Milne-Edwards, between the hydrozoal and actinozoal types, 

 yet its full value as a classificatory character still continued unappreciated. As Eschscholtz, 

 however, had seen in the reproductive system of the medusae a ground for their separation into 

 two primary groups, so in the same year Professor Rapp, of Tubingen, proposed to divide the 

 polypoid cwlenterata into two sections, also based upon the peculiarities of their reproductive 

 system." Observing that in the hydroid trophosome the ovigerous buds were produced externally, 

 while in Actinia and the corals the reproductive organs projected into the interior of the Ijody- 

 cavity, he assumed this diiference as a basis for the definition of two distinct groups, to which 

 he gave the names of Endoarii and Exoarii. Though the real nature of the peculiarity on which 

 this dismemberment of the fixed ccelenterata rests was, like that in accordance with which 

 Eschscholtz had already based his subdivision of the Medusae, scarcely comprehended by its 

 author, the proposal of Rapp must, nevertheless, be regarded as an important step towards the 

 determination of the systematic position of the Hydroiua. 



Among the results of Milne-Edwards's investigations carried on in the Chausey Isles, the 

 most important was his demonstration of a type of structure in the Flustrce, entirely diflerent 

 from that of the ccelenterate animals with which they had been associated by his predecessors. 

 A similar conclusion had been just arrived at by Grant,^ but the British zoologist had not 

 worked out the structure with that completeness which characterised the investigations of 

 Edwards, who now showed* that the Flustra were constructed on a plan in all essential points 

 identical with that of the compound Ascidians, with whose organisation Savigny had already 

 made us acquainted in his masterly memoirs. 



Though M. Milne-Edwards had thus proved the existence of a true molluscoid type of 

 structure in Flustra, no comprehensive name had yet been given to the group so characterised. 

 While Grant and Edwards, however, were thus engaged in their anatomical examination of 

 Flustra, J. V. Thompson, then residing on the coast of Cork Harbour, was occupied with a series 

 of similar investigations, and, quite independently of any knowledge of the labours of Grant and 

 Edwards, had determined not only tlie molluscoid structure of Flustra, but had in a very complete 

 way demonstrated an entirely similar structure in other plant-like organisms hitherto associated 

 with true ccelenterate forms. To the organisms thus characterised by this common type of 

 structure Thompson, while fully recognising their relation to the Ascidians, gave, in 1830, the 

 name of Volyzoa:' 



^ J. Victor Audouin and H. Milne-Edwards, " Resume des Recherches sur les Animaux sans 

 Vertebres, faites aux Isles Chausey," ' Ann. des Sci. Nat,,' 1838. 



^ Wilhel. Rapp, ' Ueber die Polypeu in AUgemeinen und die Actinien insbesondere,' Weimar, 1829. 



■' Robert E. Grant, " Observations on the Structure and Nature of Flustrse," ' Edinb. New Phil. 

 Journ.,' vol. iii, 1827. 



* Op. cit. 



' John Vaughan Thompson, 'Zoological Researches and Illustrations,' Cork, 1830. The date is 



