NATURE AND AFFINITIES OF THE SPONGES. 1 47 



completely metamorphosed or obliterated. Excepting, in fact, his notice 

 of the several observations of Grant, Dujardin, Carter, and Liebcrkuhn, 

 concerning the presence and disposition of the monociliated sponge-cells, 

 Dr. Bowerbank's only personal record of their definite recognition is asso- 

 ciated with the calcareous type Grantia compressa, of which species he 

 figures and describes their characteristic tesselated plan of arrangement. 

 In their isolated condition the separate flagellate elements are so delineated 

 as to resemble the spermatic cells of ordinary vertebrate animals, having a 

 small ovate body and a long and comparatively thick terminal flagellum. 



With the year 1866, an important epoch in the elucidation of the 

 structure and affinities of the Spongida was inaugurated. In June of that 

 year was published in a condensed form in the ' Proceedings of the Boston 

 Society of Natural History,' the results of a prolonged and painstaking 

 investigation instituted by Professor H. James-Clark, of the Agricultural 

 College of Pennsylvania, U.S.A., with reference to the ultimate form and 

 composition of the monociliated cells of a calcareous sponge most nearly 

 allied to the Leucosoleiiia botryoides of Bowerbank, and having respect to 

 their close correspondence with the individual zooids or units of certain 

 new forms of Flagellate Infusoria which he had recently discovered and 

 then described for the first time. This important communication, with 

 accompanying plates, appeared in extenso in the ' Memoirs ' of the above- 

 named society, vol. i. plate iii., for the year 1868. The essential feature of 

 the new and special forms of Flagellata here introduced, numbering in all 

 four species, and referred to the then two newly instituted genera Codosiga 

 and Salpingceca, consisted of the fact that all of their representatives were 

 provided at the free anterior extremity with a delicate funnel-shaped ex- 

 pansion of the sarcode, possessing an extraordinary amount of plasticity. 

 which in its normal condition of expansion surrounded the base of the 

 flagellum. 



Upon this newly discovered and remarkable structural element Professor 

 Clark bestowed the appropriate title of the " collar," and as " collared " or 

 "collar-bearing" monads, the animalcules then and since discovered sharing 

 a corresponding structure, are now generally known. Turning his atten- 

 tion to the ultimate ciliated elements of the calcareous sponge just 

 mentioned. Professor Clark at once recognized that when viewed with a 

 sufficiently high magnifying power they exhibited a type of organization 

 precisely identical with that which obtained in the independent collar-bearing 

 monads, possessing like these a similar film-like, extensile and contractile, 

 collar-like membrane, enclosed terminal flagellum, posteriorly located con- 

 tractile vesicles, and all other details characteristic of an isolated monad 

 of his newly established genus Codosiga or Salpingceca. As indicated by 

 Professor Clark, any one previously acquainted with the structure of 

 Codosiga, but not with the sponge, would without doubt, in describing 

 merely the congregated monads of the latter, pronounce them to be colonial 

 and massive growths of the previously named simple Flagellata. The other 



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