and boring marine animals. 369 
to the supposition of penetration by a mechanical force, the 
failure of the experiments cannot be considered to militate 
very strongly against the only inference to be drawn from 
the facts. I regret my inability to offer the last decisive 
proof, which would have set the question finally at rest ; but 
I feel persuaded that, should future enquiries be successful in 
ascertaining facts which have escaped my observation, they 
will tend to substantiate the conclusion which I have been led 
to support. 
EXPLANATION OF THE FIGURES 
PLATES XIV, XV. 
Fig. 1. The Terebella conchilega, as it appears when 
proceeding to collect materials for its tube ; <2, the mouth ; 
b b, the larger scales below the head, with which it fixes the 
materials of its tube ; c c c, the course of one of the muscles 
by which the animal throws itself into folds. In specimens, 
which have been deprived of food for a few days, the mus- 
cular fibres become beautifully distinct. 
The figure given by Pallas, and which is I believe the 
only one we possess, is not only drawn from a bad specimen, 
but is so very carelessly engraved, as to be inaccurate in 
almost every respect. 
Fig. 2. A burrowing bivalve ; Lutraria compressa : the 
left valve, syphon, mantle, and branchiae removed. 
a, The anterior, and b, the posterior muscles of the foot ; 
c, the course of the tube by which the foot is distended with 
water ; d and e, the adductors. 
Fig. 3. The animal of Buccinum undatum ; part of the 
