282 Dr. W.C. M‘Intosh on the Boring of certain Annelids. 
chalk and limestone, the empty perforations, however, do ex- 
hibit a form somewhat like a keyhole in transverse section ; 
but in the calcareous rocks and stones containing living speci- 
mens the double tube is completed by an intervening column 
of débris, except at the loop. In not a few of the worn pieces 
of chalk and limestone, only the widened inferior end or junc- 
tion of the tube remains. ‘This is a point of some interest, 
since Dodecaceria concharum abounds in the same sites, and its 
gallery is distinguished in transverse section by having no in- 
curvation, or only a very slight incurvation in the middle, and 
is not double; yet the dried remains of this worm might most 
aptly be described “ as a black carbonaceous film,”’ whereas the 
dried remnants of Leucodore are of a pale or straw-yellow hue. 
Amongst the minute fragments of flint which form the 
fine gravel of Luccomb Chine, in the Isle of Wight, are 
many loose rounded pieces of limestone and chalk more or 
less perforated by Leucodore and Dodecaceria; but the living 
examples of the former occur chiefly between half tide and 
low-water mark, the best site being at the verge of the latter, 
and this more especially as regards Dodecaceria. Leucodore 
is not only abundant in the substance of the rocks themselves, 
as mentioned by Mr. Lankester, but swarms under the spread- 
ing base of Corallina, though, on account of the inconspicuous 
nature of the apertures in the latter, little or no trace of the 
borings can be observed until the surface is split off. Besides, 
in this (littoral) region there are numerous flattened stones, 
one or two feet square, that have their surfaces quite worm- 
eaten by the perforations of the Annelids, whose now vacant 
galleries have been considerably enlarged by the action of the 
sand and surf. Occasionally the borings in these large stones 
were arranged in a linear series, the worm having attacked 
the commencing fissures as the most vulnerable parts of the 
mass. At White-Cliff Bay, again, the perforations in the 
chalky rocks abounded in the same region, and were of a 
somewhat larger size than those made by our northern ex- 
amples. 
Descriptions of the general structure of Leucodore have been 
published by the Abbé Dicquemare, Dr. Johnston, MM. Cirsted, 
Grube, Claparéde, and Keferstein; so that my remarks at pre- 
sent shall be confined to the tentacles, bristles, hooks, and 
anal segment. 
The tentacles (Pl. XIX. figs. 1 & 2) are a pair of very mobile 
muscular organs, possessing in each case a ciliated furrow on the 
inner side, Dr. Johnston being in error in averring that the in- 
ferior side is so supplied. Dr. Strethill Wright* has given a 
somewhat minute account of their microscopic appearance in 
* Edinb. New Phil, Journ. 1857, vol. vi. p. 90. 
