JJ3?3 Mr. A. Hancock on the Excavating Sjwnffes, 



internal membranes, and occur also in the papillse, where they 

 are frequently arranged transversely. The minute spicula are 

 found everywhere, but in the greatest number in the external 

 membrane, particularly on the papillae; they are sometimes 

 crowded together in vast multitudes. In the species which have 

 only pin-like spicula, these spicula equally pervade all the mem- 

 branes ; but I have not observed that they assume any definite 

 arrangement in the papillae, though in C. globulifera, one of the 

 species described in the sequel of this paper, which has only the 

 pin-like form, they are occasionally arranged in^ a radiating 

 manner in the internal membranes. Thus it appears that^ in 

 some instances at least, Cliona does show a limited degree of 

 order in the distribution of the spicula. 



It must not, however, be supposed that the spicula supply 

 the only characters that distinguish the species : the colour of 

 the sponge must also be taken into account, as well as the size, 

 number, and distribution of the papillae; the general habit and 

 mode of branching, or, in other words, the size and character of 

 the burrows containing the sponge are highly characteristic. 

 But here, again, we are unfortunately at issue with Dr. Bower- 

 bank, who asserts that these burrows are made by "lithodomous 

 Annelids"*, and consequently the branching of the sponge must 

 be accidental, being entirely dependent for its character on the 

 form of the cavities within which the sponge is lodged, being 

 moulded, in fact, in worm-burrows. I shall not here reiterate 

 the facts and arguments brought forward in my former paper 

 to refute such an opinion. It may, however, be asked how it 

 is that, while C. celata is found in vast abundance on our coasts, 

 inhabiting excavations in shells and limestone, the worm or 

 annelid assumed to have made the cavities has never yet been 

 determined. Surely, if these are worm-burrows, we ought 

 naturally to expect to find the maker of them, as frequently at 

 least as Cliona, in peaceable undisputed possession of its habita- 

 tion. But no, Cliona alone occupies these cavities ; no worm 

 has yet been taken that the naturalist can pronounce to have 

 made them. Then why not allow Cliona to be the fabricator, as 

 it is the constant possessor, of its excavated home ? 



Dr. Bowerbank, indeed, mentions "severaP' instances of 

 having found Annelids occupying the " numerous sinuous 

 canals" in large Balani from the Guliot caves in Sark, and also 

 of finding " living Annelids in deeply seated portions of the 

 perforations in the limestone boulders of Tenby "f- There is 

 nothing surprising in this; in fact we might have expected 

 such instances to occur much more frequently to a naturalist 



* 0/7. ci7. vol. ii. p.221. "[Ibid. 



