Am) PHYSIOLOGY OF THE SPOHGIAHH:. 
781 
that of a rosette. Fig. 10, Plate XXXI. represents a rosette-shaped group containing 
about the usual number of spicula. 
Besides the rosette-shaped groups in Halichondria lingua^ there are a considerable 
number of these spicula dispersed over the surfaces of the membranes ; but the attachment 
of these spicula is more frequently at the middle of the shaft than at the smaller end of the 
spiculum, their normal point of attachment. In the single and separate mode of dispo- 
sition they are performing the office of equi-anchorate spicula, and the mode of their 
attachment is varied accordingly ; but under these conditions they are rarely ever so fully 
developed, nor do they attain the same size as those which form the radiating groups. 
Notwithstanding the numerous groups and dispersed spicula of the inequi-anchorate 
form, this sponge is also abundantly furnished with bihamate spicula of various forms, 
but they are never congregated like the anchorate ones. 
The same radiating mode of arrangement occurs in a parasitical Australian sponge 
from Freemantle, but the form of the terminations of the spicula is very ditferent from 
those of Halichondria lingua. The distal termination of each of the inequi-anchorate 
spicula is shortened in length, but expanded laterally to a considerable extent, and its 
terminal edge is furnished with three thin pointed teeth. The distal end has two small 
expanded and raised wings, projected in the direction of the inner curve of the spiculum, 
and so disposed as to cause it to resemble very closely an engineer’s spanner for bringing 
up to their bearings projecting square-headed screws. Thus, although the forms of the 
termination of the two varieties of spicula vary to a considerable extent, the principles of 
their structure and purposes are in perfect unison. Fig. 11, Plate XXXI. represents a 
group of these spicula, and fig. 12, Plate XXXI. a single spiculum highly magnified to 
display their peculiarity of structure. 
These forms of spicula appear to be peculiar to the siliceous sponges. I do not recollect 
having ever seen them in any species of calcareous sponge. 
S;picula of the Sarcode. 
The primary office of the whole tribe of multiradiate spicula is evidently that of con- 
solidating the sarcodous substance of the sponge, nor is their presence in the exercise of 
this office confined to the Spongiadse. In the soft parts of the extensive family of the 
Gorgoniadse we find them in vast abundance, and in every variety of form, from an 
elongate tubercular spiculum to the elongo-stellate forms of the Spongiadae, and the preva- 
lence of the bluntly terminated radii is strongly indicative of their non-defensive character. 
But this latter quality does not obtain in other cases, either as regards the higher tribes 
of animals or the Spongiadae. Thus we find in numerous species of compound tunicated 
animals their fleshy substance is crowded with sphero-granulate spicula, very closely 
resembling in form those of the sphere- and subsphero-stellate shapes so abundant in 
Tethea Ingalli and T. rohusta (figs. 14 15, Plate XXV. Phil. Trans. 1858). In both 
these cases the acute termination and the peculiarities of their respective situations are in- 
dicative of their subserving the office of defensive, as well as that of consolidating spicula. 
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