324 Mr. A. Hancock on the Excavating Powers of Sponges, 
species. And the three individuals of C. corallinoides that I have 
procured are buried in as many specimens of Pecten maximus. 
All these cases, however, may arise from similarity of locality, 
and not from any partiality to the species. ; 
The boring sponges, as far as | have examined them, are 
branched, or are composed of lobes united by delicate stems ; 
and all more or less anastomose according to the species: many 
of them are beautifully arborescent and of great delicacy*. They 
all bury themselves im shells or other calcareous bodies, and 
communicate with the water by papille or oscula protruding 
through circular holes in the surface of the containing substance 
or matrix. In dead shells the papille pass through both surfaces, 
but in living ones rarely penetrate the innermost layer, though 
occasionally they do so. When a mollusk is thus wounded it 
deposits calcareous matter over the orifice, and generally succeeds 
in excluding the intruder. The species vary considerably im form, 
and in Clhona might be divided into two or three distinct groups. 
In some the branches are almost linear, and anastomose only to 
a very slight degree; others form a complete network with the 
meshes so small that very little of the matrix remaims between 
the branches; some have the branches moderately lobed; and 
others again have the lobes large and crowded upon each other 
im all directions, and united by fine, very short stems. In most 
the terminal twigs are very minute, and exhibit im a decided 
manner the mode of growth. In C. gracilis, for example, we per- 
ceive that they are eylindrical, and divide dichotomously, and 
that afterwards they augment in thickness gradually and pretty 
regularly, there being only slight indications of a lobed structure. 
In C. corallinoides, Pl. XY. fig. 1, the twigs are excessively mi- 
nute, passing onward for some distance through the sound shell ; 
and as they increase they become gradually lobed, the lobes ulti- 
mately attaining considerable size and becoming quadrate. This 
mode of growth is common toa great number of species : in some 
it is beautifully modified, as we see in C. spinosa, Pl. XIII. fig. 5 ; 
here the terminal twigs are mostly short and pointed, resembling 
spines thrust out from all sides of the close-set lobes; which 
spines or twigs in their turn swell out and become lobes. But 
of all the excavating sponges, Thoosa cactoides, Pl. XIII. fig. 1, 
* Dr. Johnston describes C. eelata as ‘‘ without beauty or definite form ;” 
but the specimens he examined may have been of abnormal growth, result- 
ing perhaps from the entire destruction of the substance which had inclosed 
them. The Doctor's species however appears to be distinct from the C. celata 
of Grant, judging by the spicula, which, according to the figures of them by 
Mr. Bowerbank, are perfectly straight. In the-species described by Pro- 
fessor Grant they are stated to be ‘slightly curved and_a little fusiform in 
the middle.” 
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