62 E. W. RUATT ALY. 
filaments as respiratory organs were faulty as they made no allowance for 
the animal’s natural habitat. The réle played by the filaments is essen- 
tially respiratory ; further, close observation has shown that the prehensile 
function, so readily admitted by most authors, is non-existent. Careful 
study of the animal’s habits shows that there is absolutely no need for 
such a function, whereas there is every need for that of respiration. What 
leads the majority of observers to suppose a prehensile function is un- 
doubtedly the perpetual curling motion of the filaments in the pools. A 
differentiation of function between the lateral filaments and those in the 
paired fascicles is undoubtedly suggested by their behaviour when the 
animal is withdrawn from the mud. The filaments in the clusters im- 
mediately contract, their colour becoming quite yellow, while the remain- 
ing lateral filaments are still more or less distended by the contained blood, 
and are, of course, red in colour. These superficial differences, however, 
do not necessarily prove any difference in function, and this notwithstand- 
ing the disparity in structure referred to by Bounhiol. [It has been sug- 
gested that the fascicles of filaments are prostomial tentacles which have 
shifted backwards, Meyer (12)]. The worm is essentially and in all except 
pertectly abnormal conditions a burrower, and consequently permanently 
subject to pressure. Whenall pressure is relaxed and the animal bathed on 
all sides by water it is only natural that, with respiration taking place over 
the whole body surface, numbers of filaments should be left idle, and it 
would be particularly the filaments lying in front of the heart-body which 
would be affected. In further response to the relieved pressure the animal 
contracts and curls up, the anterior part of the body is forced beneath the 
coils and the prostomium is protruded as far as possible, and the charac- 
teristic actions of burrowing are performed, that is to say, the anterior 
region is pumped turgid with fluid and waves of muscular contraction 
pass along the body from behind forwards. At the same time the mucous 
investment, with the sand adhering from the burrow, is gradually shed 
and becomes caught in the gill filaments, and an inextricable tangle is the 
result. Prof. McIntosh notes that the animal appears to be less comfort- 
able in pure sea water, and thinks the mud to be the most fitting medium, 
since it keeps the filaments apart. Undoubtedly, mud is a more fitting 
medium, but not, I think, for this latter reason. If a number of flat stones 
be laid upon the bottom of the vessel, the worm, a few hours later, will be 
found ensconced beneath them and numbers of filaments will stretch in 
all directions, without any trace of entanglement, showing that what the 
animal chiefly lacks is pressure. 
The appearance of the gill filaments when the worm is in its natural 
habitat is sufficiently familiar, but the manner in which they attained 
that position, in view of their extreme delicacy, is rather remarkable. If 
