Untitled

152 NATURE AND AFFINITIES OF THE SPONGES.science, the latest evidence in this direction, a few months prior only tohis much-to-be-lamented decease, was produced by Professor Clark himself.Already, in 'Silliman's American Journal' for February 1871, hehad drawn attention to Cienkowski's new social monad genus Phalanstcrium,and indicated its apparent close affinity to the collared types Codosigaand Salpingoeca discovered by himself, but from which they differed mostessentially in the less conspicuous development of the characteristic collar,and in their social or colonial occupation of a common gelatinous matrix.This latter point more especially was cited as indicative of a still moreintimate relationship with the sponges than that presented by the two lastnamedgenera. Professor Clark further placed on record in the same serialthe results of his recent investigations into the ultimate structure of theAmerican Fresh-water Sponge, Spongilla arachnoides J.-Clk., the resultsconfirming substantially, and adding considerably to, the data elicited throughhis previous examination of the marine calcareous type Leucosolenia botryoides.In this fresh-water form, however, the characteristic collared flagellatecells were found occupying definite spherical excavated chambers, correspondingwith those described by Mr. Carter of Spongilla alba under thename of ampullaceous-sacs, which received from Professor Clark the equivalenttitle of the " monad chambers." Taken in its entirety, the spongebodyof this species was declared to be composed of the three followingdistinct and well-marked elements :Firstly, of a common, glairy, gelatinousbasis, within which all the remaining constituents were embedded, andwhich he designated the cytoblastema. Although presenting the samecharacteristic consistence throughout, this glairy cytoblastema exhibited aseparation into two distinct regions, the one consisting of a thin superficialstratum, stretched out on the points of the larger externally projectingspicula, after the manner of a tent-canvas extended upon the ends of itssupporting poles. Within this peripheral cytoblastematous layer, designatedby Professor Clark in its separate form the " investing membrane," there wasno trace to be found of the monad-chambers. These latter, which constitutedthe second and most important structural element, were confinedentirely to the deeper and comparatively solid substratum of the cytoblastema,and which he therefore distinguished, with relation to its contents, asthe " monadigerous layer." The third and remaining essential element recognizedby Professor Clark consisted of the innumerable amoebiform cells orbodies scattered more or less abundantly throughout the substance of thecytoblastema, and most conspicuously visible, in consequence of the absenceof the monad-chambers, in the thin superficial stratum or so-called investingmembrane. These amcebiform cells were distinguished by Professor Clarkmerely by the name of the " cell-elements " of the cytoblastema, but, forconvenience, may be " "appropriately designated the cytoblasts or"cytodes." Like simple cytodes, they were shown, as also pointed out byProfessor Haeckel, to possess no distinct cell-wall, and, unless speciallyfocussed for, were scarcely to be distinguished from the cytoblastema in