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NATURE AND AFFINITIES OF THE SPONGES. 145polymorphic and flagellate cells first noticed by Dujardin. To a like categorymust undoubtedly also be relegated the so-called "spermatic elements,"described by Professor Huxley in the 'Annals of Natural History' for theyear 1851. Lieberkuhn* corroborated and added considerably to thedetails of the structure and life-history of Spongilla made known byDujardin, and elicited much new evidence concerning the occurrence inthis type of the motile ciliated germs, in addition to the more ordinarilyoccurring non-motile and so-called "seed-like bodies," first discovered byDr. Grant, in association with various marine species, and merely recordedby Dujardin, on the authority of M. Laurent, as existing in Spongilla.Following upon Lieberkuhn's discoveries, must be recorded the veryimportant contributions respecting the ultimate structure of the closelyallied Indian species of Spongilla, contributed by Mr. Carter to the'Annals and Magazine of Natural History,' during the years 1857 and1859. In the first of these contributions, the entire life-history, from theindurated " seed-like body " up to the adult state, was successfully tracedout, and many entirely new facts respecting the more minute histology ofthe sponge organism elicited. Among these it was demonstrated that theessential living constituents of the sponge-body were represented by theciliated monad-like elements first described by Dujardin, and that theyexhibited a very definite mode of arrangement. Under normal conditions,Mr. Carter found that the monad cells were congregated together so astoform a single and even layer within the interior of small spherical chambersexcavated within the sarcode or mucilaginous basal substance of thesponge, and to which chambers he applied the term of "ampullaceous sacs."The additional name of ovi-cells was also given to these chambers in theirearlier condition, from his having observed their development out of apre-existing ovule-like or granular mass, this latter first passinginto thenormal, small, monociliated and unciliated sponge-cells which then spreadover the interior surface of the so-called ovi-cell, each with its ciliumdirected inwards, and so leaving a cavity in the centre which finally becameconnected with the nearest adjacent afferent canal.The origin of these " ampullaceous sacs," by a process of developmentcorresponding to the growth and segmentation of an. ordinary ovum, is,as hereafter shown, entirely confirmed by the investigations of the presentauthor. Mr. Carter further demonstrated the capacity of both the ciliatedand unciliated sponge-cells of the ampullaceous sacs to take in solidfood in the form of minute granules of carmine distributed in the surroundingwater, as also the possession by these individual bodies of contractilevacuoles and nucleus-like granules. Taken as a whole, the animal natureof Spongilla was now proved beyond further question, and its compositionmaintained to consist essentially of polymorphic monadiform or amoeba-likeelements, closely corresponding with ordinary monads and amoebae, theformer being aggregated together in definite order within the structureless* 'Miiller's Archiv,' Bd. i., 1856.L