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1 68 NATURE AND AFFINITIES OF THE SPONGES.the feeding capacities of the sponge-monads, it may be here noted, thatthe phenomena of nutrition are preciselyidentical with those exhibitedby the independent collared species, the selected pabulum being arrested bythe hyaline collar and carried with its circulating current into the bodyof the animalcule. Examples are given at PI. VIII. Figs. 9 and 19, inwhich the bodies of the neighbouring sponge-monads are rilled with ingestedand artificially administered carmine particles. Such functions of nutritionare, however, not confined to the collared zooids ;the amoebiform unitsor cytoblasts being equally capable, as shown at Fig. 41 of the same plate,of ingesting solid pabulum.Examining the matter more closely, it has now to be shown that eventhe special differences already cited as indicating a distinction between theSpongida, independent collared monads, and ordinary Infusoria, are scarcelymore substantial than those found to exist between the more conspicuouslydivergent representatives of the same groups or orders of the lastnamedsection. Taking, in illustration of this analogy, the very familiargroup of the Vorticellidae, we find in Vorticella, or more correctly, in thestiff-stalked form Rhabdostyla and in the compound type Epistylis, theprecise analogues of the solitary collared type Monosiga and the socialgenus Codosiga. Proceeding yet a step further, the slime- immersed colonialtype Ophrydium is beyond doubt comparable in a like manner to thecolonial slime-immersed genus Phalansterium. Beyond this it is notpossible, as yet, to institute a direct comparison, but, supposing that agenus of colonial slime-immersed Vorticellidae should be discovered inwhich the animalcules, instead of projecting directly into the surroundingwater through the peripheral surface of their common matrix, as obtains inOphrydium, were enclosed within chambers which communicated with eachother, and with the outer water, by a system of interconnecting canals ;supposing also that all the spores, germs, encystments, or other reproductiveproducts remained embedded and developed to maturity withinthe common matrix, a type of the Vorticellidae would be produced presentinga parallel to Ophrydium precisely identical with what actuallyexists between the most simple known sponge and Phalansterium*With the assistance of Plates VII. to X. it is now proposed to draw* At the eleventh hour, while going to press, the author has had the good fortune to light upona new and highly interesting representative of the independent collared series, that illustrates ina yet more decisive manner the close relationship of this group to the Spongida. The type inquestion, represented at PI. X. Figs. 20-30, and hereafter described under the title of ProtospongiaHaeckeli, agrees with Phalansterium, so far as the zooids are immersed within a common gelatinousmatrix or zoocytium. The characteristic collars are, however, fully developed in place of beingrudimentary as in the last-named genus, while the inhabited gelatinous matrix is perfectly transparentand homogeneous instead of densely granular. Within their matrix the zooids were observedto assume various metamorphic amoeboid conditions, to multiply both by the process of binarysubdivision and by the partition of their entire mass into sporular elements. The resultants ofthe last reproductive process commence their active existence as simple, minute, uniflagellatemonads, which project, as shown at Fig. 22 b b, from the periphery of the zoocytium side byside with the adult collared units. This interesting species which, in its mature condition, correspondsin a most remarkable and significant manner with a fragment of cytoblastema, with itsenclosed collared zooids, amcebiform cytoblasts, and sporular elements, of any typical spongeform,was obtained by the author in July 1 880, in water brought from the lake in Kew Gardens.