342 MR. ALBANY HANCOCK ON" 



the limestone boulders of Tenby. "* There is nothing surprising 

 in this ; in fact, we might have expected such instances to have 

 occurred much more frequently to a naturalist of Dr. Bower- 

 bank's experience. Many worms and other marine animals 

 conceal themselves in any hole or crevice they can find, and 

 numerous worms or annelids perforate both shells and limestone, 

 and other hard calcareous bodies. Living worms, occupying 

 their own burrows in these substances, are frequently met with ; 

 and it is not uncommon to find such burrows in shells perforated 

 by Cliona, and mingling, in the most intricate manner, with the 

 excavations of the latter. But there is never any difficulty in 

 determining which was made by the worm, which by the sponge, 

 xind if the instances mentioned in the " Monograph of the British 

 Spongiadas" are genuine worm-burrows, neither can there be, in 

 these cases, any uncertainty as to the fact of their being so. 



"Worm-burrows are always linear, usually cylindrical, and are 

 more or less tortuous : they never assume a dendritic form, are 

 sometimes double, or as it were bent upon themselves, and a 

 little flattened ; the surface is invariably smooth, never punc- 

 tured or shagreened, as it is in the burrows of Cliona, the exca- 

 vations of which, on the contrary, are always dentritic, dividing 

 dichotomously, anastomosing, usually constricted at intervals, by 

 perforated septa, so as to form a congeries of small chambers, 

 and having the surface constantly punctured or shagreened, and 

 generally giving off, on every side, numerous delicate ccecal tubes. 



To account "for the vast number of perforated shells, and the 

 comparative rareness of the annelids," it is suggested in the 

 work on the British Spongiadse before quoted, f that the worms, 

 assumed to have made these perforations, obtain their nutri- 

 ment by passing the excavated substance, " abounding in animal 

 matter," through the digestive organs; the analogy of the earth- 

 worn being relied on. Unfortunately, however, for the advocacy 

 of such an idea, the excavations inhabited by Cliona are of the 

 same character, and equally extensive in limestone. "Whatever 



* "Monograph of the British Spongiadse." Vol. II, p. 221. 

 f " Monograph of the British Spongiadas." Vol. II, p. 220. 



