NATURE AND AFFINITIES OF THE SPONGES. 171 



be proceeded with. As previously maintained, between the separate collar- 

 bearing monads of any of the independent Choano-Flagellata and the special 

 collar-bearing cells that constitute the one essential element of all sponge 

 structures, there is absolutely no recognizable distinction in form, structure, 

 and function. The body with its nucleus or endoplast, multiple contractile 

 vesicles, and appendages as represented by the characteristic collar and 

 enclosed flagellum, so precisely accord with each other as to defy individual 

 identification, a circumstance which will be at once recognized on comparing 

 these collared elements in their isolated or aggregated form, as abundantly 

 illustrated in the Plates VII. to X. and II. to VI., devoted respectively 

 to the morphology of the Spongida and that of the independent collared 

 monads. The likeness, however, does not end, but practically only com- 

 mences here, for, as it has now to be shown, all the phenomena of 

 reproduction and development are likewise reducible to a corresponding 

 type. 



In order to fully comprehend and appreciate the full force of this 

 relationship, it is requisite only to place still more intimately en rapport, 

 the life-phenomena of the collar-bearing sponge-monads and those of the 

 independent Choanophorous and ordinary Flagellate Protozoa. That the 

 thin, structureless cytoblastema forming the common gelatinous matrix 

 which encloses and more or less completely conceals the collar-bearing 

 monads of the sponge-body, is the equivalent of the common gelatinous 

 matrix of such genera as Phalansterium and Spongomonas, or, reverting to 

 a still more familiar ciliate infusorial type, that of Ophrydium, is imme- 

 diately apparent, and is similarly, as hereafter shown, the direct product 

 by exudation of the included zooids. By Professor Haeckel this common 

 gelatinous element in sponge structures is denominated the "syncytium," 

 and treated of as an independent tissue-layer formed by so intimate a 

 coalescence of independent constituent cells that their nuclei only are to be 

 discerned. That a syncytium, however, in the sense assumed by Haeckel, 

 does not exist, is abundantly proved by the testimony accumulated from a 

 variety of sources ; what he embodies under this title represents in point 

 of fact both of those fundamental elements which receive in this volume 

 the titles of the " cytoblastema " and " cytoblasts." It is to the existence 

 and significance of the last-named elements that attention has now to be 

 directed. The characteristic aspect of the cytoblasts which occur as 

 amoebiform bodies of variable size and contour, variously distributed and 

 more or less completely immersed within the substance of the cytoblas- 

 tema is delineated at PI. VII. Fig. 2 c and PI. VIII. Figs. 41 to 43. Like 

 Amoeba, they are constantly undergoing a change of outline, and may also 

 be observed to shift their position from one part to another of the inhabited 

 matrix or cytoblastema. Oftentimes their long, slender pseudopodia, radi- 

 ating towards those of their neighbours, unite together, forming under 

 such conditions a complex network which presents, as a whole, as shown at 

 Fig. 43, a remarkable resemblance to ganglionic corpuscles ; these highly 



