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PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION

features leading to the same conclusion. The structure of the latter forms is diffe-rent from that of any existing Radiolarians . Instead of possessing the fenestratedskeleton which would allow the calcareous ooze, constituting the matrix, to penetratefreely into the interior of each sphere-cavity, all such intruded material has beenabsolutely excluded from those cavities. The interior of each is occupied, not byamorphous matter like the investing matrix, but by crystalline calcic carbonate, asolution of which had obviously filtered through the porous sphere-wall, and crystallizedwithin the interior of a closed cavity. In this respect the conditions of the objectscorrespond exactly with those of the carboniferous Foraminifera , which I find associatedwith them; I am convinced that no known Radiolarian would exhibit similar con-ditions. Then their form is more like that of the Foraminiferous Orbulina than anyRadiolarian . Occasionally chance sections like figs. 73 and 76 remind us of a Dictyoca ;but other specimens, such as figs. 74 and 77, show that these apparently regular sym-metrical forms and arrangements of the spines are not characteristic of the organisms.Even in fig. 7 6 the second unsymmetrical spine to the right hand of the figure is fatalto the idea of the object being a Dictyoca. It is obvious that these organisms wereclosed spheres with a sphere-wall so nearly solid as to exclude all inorganic matter savesuch crystalloids as were in a state of solution, and which, consequently, were capableof reaching the sphere-cavity by infiltration.

But a further difficulty stands in the way of our regarding these objects as Radio-larians . Unable generally to accept Mr. Sollas’s hypothesis of the replacement ofsilica by calcareous matter, I am still less able to do so in the case of the objects underconsideration. I have already said that such a hypothesis is wholly inapplicable tothe V. robusta (fig. 81), and it appears to me equally so to the other forms. Mr. H.Brady has arrived at the same conclusion. But anxious to obtain the opinion of someof our leading chemists on this point, I showed my specimens to Professors IIoscoe andSchorlemmer, and they both express their inability to understand how such a sub-stitution could take place. I presume that on the subject of organic chemistry no higherauthority than Professor Schorlemmer could be appealed to. After examining myspecimens, he writes to me as follows : “ I don’t know what morphological evidence youmay possess rendering it probable that the minute calcareous objects in limestone thatyou showed me were originally siliceous an im als or organisms; but I should requiresuch evidence to be overwhelmingly strong before I should accept such a conclusion.I know of no agency by which siliceous structures could be converted into calcareousones, by mineralogical substitution, under the condition in which these organismsexist, embedded'in a calcareous matrix. The fact that the silica was of animal origin doesnot appear to me to render the possibility of such a substitution more probable.”* Ihave already shown that such morphological evidence as Professor Schorlemmerdemands is non-existant—hence I am impelled towards the conclusion that theseCalcisphcerce were calcareous, and not siliceous organisms, and consequently were not

* Jn litem, Jan. 22, 1879.