148 NATURE AND AFFINITIES OF THE SPONGES. 



elements recognized by Professor Clark as entering into the composition 

 of the complete sponge-body, manifesting its differentiation from such a 

 simple monad colony as Codosiga, were, in the first place, an externally 

 placed and excessively hyaline, glairy, gelatinous matrix, upon the internal 

 surface of which the characteristic flagellate cells were embedded, and 

 secondly, the spicular bodies found immersed within the substance of this 

 glairy matrix, and by which latter element he considered them to be 

 secreted. Upon this common matrix he conferred the title of the cyto- 

 blastematous layer, or " cytoblastema," in contradistinction to the internal 

 pavement-like one composed of collar-bearing units, and which he desig- 

 nated the monadigerous layer. The spiculae themselves he represented as 

 directly comparable with the horn-like loricae secreted, or rather excreted, 

 as protective coverings by such genera as Cothurnia, Salpingceca, and other 

 ordinary Infusoria. 



It was at once recognized by Professor Clark that the so-called spini- 

 ferous elements of Spongilla, figured and described by Mr. Carter in the 

 year 1859, were closely identical with what had been observed by himself 

 in Leucosolenia, and that the two "spines" or "ear-like" points recorded by 

 the former authority, represented actually the right and left profiles of a 

 similar subcylindrical membranous collar. Mr. Carter's observation of these 

 " spine-bearing " cells in a limited number of instances only is satisfactorily 

 accounted for by Professor Clark's record of the facility and rapidity with 

 which when disturbed this membranous collar is completely withdrawn 

 into the general substance of the body-sarcode. With reference to the 

 food-incepting phenomena of the sponge-monads, Professor Clark was not 

 able to arrive at a definite conclusion. Presuming, nevertheless, from his 

 assumed discovery of a distinct oral aperture in Codosiga and other 

 Flagellata, close to the base of the flagellum, he was led to predicate the 

 existence of a similarly located one in the case of the sponge-monads. As 

 hereafter shown, however, Professor Clark's inferences concerning the nature 

 and position of the oral aperture in both the independent and associated 

 collared monads, have not been confirmed. Summing up the results of his 

 discoveries, the views maintained by Professor H. James-Clark with refer- 

 ence to the position and affinities of the sponges were, that these organisms 

 must be regarded as compound colonial forms of Flagellata, whose units, in 

 the case of Leucosolenia, exhibited a type of structure essentially similar 

 to that of Codosiga and Salpingceca, but might possibly in other instances 

 more closely approximate to that of Monas (Spumella) Bicosceca or 

 A nthophysa. 



The entirely new light brought to bear upon the much vexed question 

 of the affinities of the sponges, and the influence upon the scientific mind 

 it was calculated to exert, through the important discoveries of Professor 

 Clark, were doomed, for a time at least, to be thrown into the back- 

 ground, if not altogether set aside, in consequence of the almost contem- 

 poraneous introduction upon the scene of a yet more novel, and for the 



