AND HABITS OF THE AMMOCHARID#. 249 
The Ammocharide are generally regarded as “ sedentary 
worms,” but, from what has been said in the earlier part of this 
paper, it will have been gathered that their habits are not 
entirely of that character. Members of this family are, in fact, 
capable of burrowing in their tubes through the sand; and 
although this is usually done without travelling far afield, still 
they are quite capable of working their way through a consider- 
able thickness to the surface, or of leaving the sand entirely, and 
reburying themselves in new sites. Experiments made with the 
object of learning something of these habits, have elicited 
interesting facts. When the worm is first captured and exposed, 
say by digging and rapidly washing away the sand by means of 
a sieve, it is generally found that the tube is of considerable 
length, firm and swollen at the part where the worm at the time 
happens to be, but diminishing to the diameter of thin twine in 
the unoccupied portion. In English specimens, the large propor- 
tion of fragments of shell in the outer sheath imparts a striking 
whiteness to the tube. A ball of sand, loosely held together by 
mucus, is commonly found covering the short length of other- 
wise naked tube at the posterior extremity. This is, doubtless, 
formed by the branchial tentacles. From the nature of the 
building-operations, it is obviously impossible for the “ Lippen- 
organ” to properly affix sand-grains underground, though there 
is ample evidence, in the form of imprints (d, Pl. 24. fig. 13), that 
this organ strengthens the membranous tube by external addi- 
tions of its secretion. If such a tube be left in sea-water, 
without sand, it will be found, after an interval of an hour or 
two, that it has entirely changed its appearance, and has become 
spindle-shaped, and only one half or even one-third of its 
original length. The worm, having drawn over itself the portion 
which was previously unoccupied, has thus caused the fragments 
of shell or sand to come more closely together and stand at 
right-angles to the length of the tube. If the specimen be now 
reburied beneath a few inches of sand, it will be found, after a 
short interval (varying of course with the thickness of the 
layer), that it has burrowed upwards, so as to bring the anterior 
end of its tube to the surface, a position which is apparently 
needful for its welfare ; and when it is remembered that, in doing 
this, the free edges of the external fragments have been so 
placed as to meet with the greatest resistance from the surround- 
ing sand, it will be realized that the operation involves great 
