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NATURE AND AFFINITIES OF THE SPONGES. 171be proceeded with.As previously maintained, between the separate collarbearingmonads of any of the independent Choano-Flagellata and the specialcollar-bearing cells that constitute the one essential element of all spongestructures, there is absolutely no recognizable distinction in form, structure,and function. The body with its nucleus or endoplast, multiple contractilevesicles, and appendages as represented by the characteristic collar andenclosed flagellum, so precisely accord with each other as to defy individualidentification, a circumstance which will be at once recognized on comparingthese collared elements in their isolated or aggregated form, as abundantlyillustrated in the Plates VII. to X. and II. to VI., devoted respectivelyto the morphology of the Spongida and that of the independent collaredmonads. The likeness, however, does not end, but practically only commenceshere, for, as it has now to be shown, all the phenomena ofreproduction and development are likewise reducible to a correspondingtype.In order to fully comprehend and appreciatethe full force of thisrelationship, it is requisite only to place still more intimately en rapport,the life-phenomena of the collar-bearing sponge-monads and those of theindependent Choanophorous and ordinary Flagellate Protozoa. That thethin, structureless cytoblastema forming the common gelatinous matrixwhich encloses and more or less completely conceals the collar-bearingmonads of the sponge-body, is the equivalent of the common gelatinousmatrix of such genera as Phalansterium and Spongomonas, or, reverting toa still more familiar ciliate infusorial type, that of Ophrydium,is immediatelyapparent, and is similarly, as hereafter shown, the direct productby exudation of the included zooids. By Professor Haeckel this commongelatinous element in sponge structures is denominated the "syncytium,"and treated of as an independent tissue-layer formed by so intimate acoalescence of independent constituent cells that their nuclei only are to bediscerned. That a syncytium, however, in the sense assumed by Haeckel,does not exist, isabundantly proved by the testimony accumulated from avariety of sources ;what he embodies under this title represents in pointof fact both of those fundamental elements which receive in this volumethe titles of the " cytoblastema " and " cytoblasts." It is to the existenceand significance of the last-named elements that attention has now to bedirected. The characteristic aspect of the cytoblasts which occur asamoebiform bodies of variable size and contour, variously distributed andmore or less completely immersed within the substance of the cytoblastemais delineated at PI. VII. Fig. 2 c and PI. VIII. Figs. 41 to 43. LikeAmoeba, they are constantly undergoing a change of outline, and may alsobe observed to shift their position from one part to another of the inhabitedmatrix or cytoblastema. Oftentimes their long, slender pseudopodia, radiatingtowards those of their neighbours, unite together, forming undersuch conditions a complex network which presents, as a whole, as shown atFig. 43, a remarkable resemblance to ganglionic corpuscles ;these highly