( H3 ) 



CHAPTER V. 



NATURE AND AFFINITIES OF THE SPONGES. 



It is proposed to devote the present chapter to an extensive discussion of 

 that near relationship of the sponges to certain of the Infusoria Flagellata, 

 briefly referred to on several occasions in the course of the preceding 

 pages. This affinity is found, indeed, upon an impartial examination of 

 the data here collected, to be so comprehensive and thoroughgoing as to 

 render absolutely unavoidable the correlation of this group with the typical 

 representatives of the flagellate Protozoa. Those differences which do 

 exist between the two groups are, in point of fact, far less essential than 

 those which obtain between many of the subordinate sections of the ordinary 

 Ciliate and Flagellate Infusoria; such being the case, the present work 

 could not be considered complete if it did not embrace a more or less 

 extensive account of the fundamental plan of organization, at least, of the 

 Spongida. Strictly speaking, the sponges, throughout all their wealth of 

 form and organization, are here accepted as Mastigophorous Protozoa, and 

 it is on account only of the limited space at disposal, that their full specific 

 enumeration and description, on a scale corresponding with that allotted to 

 the more typical representatives of the Flagellate Infusoria, is here omitted. 

 Under existing circumstances, it is found possible to submit a brief sketch 

 only of those broad fundamental characters which either unite with, or 

 distinguish the members of the sponge-tribe from their nearest allies, 

 supplementing them with the author's personal interpretation of those 

 somewhat obscure structural and developmental points which have been 

 held by other authorities to indicate an affinity in a difl"erent direction. 

 For, although it is confidently anticipated that the evidence now brought 

 forward must materially assist in securing to the sponges, eventually, a 

 general recognition of their intimate relationship to the Choanophorous 

 section of the Flagellate Infusoria, it can by no means be said that such an 

 affinity is at the present date universally recognized. On the contrary, 

 the balance of contemporaneous scientific opinion favours the relegation 

 of this organic group to the division of the Metazoa, though upon grounds 

 which, plausible as they seem to be upon the surface, are fundamentally 

 purely artificial and untrustworthy. 



In order to arrive at a position permitting a thoroughgoing and 

 impartial appreciation of the very voluminous and conflicting evidence 

 that has been amassed with reference to the much debated affinities of 



