236 Mr. E. R. Lankester on Lithodomous Annelids. 
chitinous setae would be of much avail against hard limestone. 
Mr. George Busk, at the meeting of the British Association at 
Dundee, suggested in discussion that the perforation was pos- 
sibly effected, both in this case and in that of Leucodore which 
I then described, by means of sand rubbed by the worm against 
the rock or introduced into its gallery when once begun. 
This he had witnessed in Pholas. The objection to such a 
view in the case of either of the Annelids is, that they do not 
possess the necessary power of lateral movement, or any 
point d’apput, also that they only bore carbonate of lime; 
and, further, it is impossible to guess how an attack could be 
commenced on a stone in such a manner. We are reduced to 
the theory that the gallery of Sabella is formed by the con- 
stant apposition of the tail of the Annelid to the carbonate 
of lime. The tail has been proved to be acid, and is therefore 
a perfectly sufficient cause. 
The boring Leucodore is represented in Pl. XI. fig. 7; and 
it will be seen that, whilst the ordinary bristles are situate on 
each somite, the fifth alone possesses very thick dark-coloured 
setez, more or less blunt at the point (fig. 9). We cannot sup- 
pose that these have any effect in perforating limestone, since 
they are merely chitine, and, moreover, are present in species 
of Leucodore which do not perforate, and which live by hun- 
dreds in the silt filling cracks of rocks &c., or construct for 
themselves rough and fragile tubes. At the same time ney 
may very possibly be efficient in excavating loose material. 
They are undoubtedly homologous with the dark bristles pre- 
sent in the anterior region of Chetopterus, and perhaps are 
only rudimentary organs—Nature’s certificate of a long pedi- 
gree. The sand-theory fails in the case of Leucodore for the 
same reason as in that of Sabella. In fact no mechanical ex- 
planation of the perforation will account for a chemical selec- 
tion of material. In every case of Leucodore-perforation to 
which I have alluded, and with dozens of fragments from va- 
rious stones, often presenting the most different appearances, 
and looking more like sandstone than limestone, I have tested 
for the presence of carbonate of lime, and have invariably 
found it in large quantity; all the fragments which I sub- 
mitted to analysis were rapidly disintegrated under the action 
of weak acetic acid. Another fact in favour of chemical action 
is the extremely clean and sharp character of the galleries, 
both in Sabella and Leucodore. 
My friend Dr. M‘Intosh was the only observer at Dundee 
who expressed a belief that these Annelids perforate rocks 
other than carbonate of lime. He said that he had seen 
aluminous shale so bored; but I think he had other excava- 
