TRANSACTIONS OF SECTION D. : 513 
the small end protruding from and the wide end buried beneath the sand, the 
animal vigorously digging its way by means of the beautiful gold-coloured 
combs with which its head is endowed. In a memoir written in 1903 it was 
shown by Fauvel that the water necessary for respiration, and also for the pur- 
pose of stirring up the sand-grains beneath the surface, is, by a kind of peristaltic 
action of the animal, drawn or pumped through the tube, entering through the 
fine pointed end exposed above the surface, and often escaping to the surface 
of the sand through the fissures formed in the digging process. It was also 
observed by Fauvel that the worm has the power to reverse the direction of this 
current at will. It-has hitherto been thought that the object of this reversed 
current was mainly to eject from the tube the sand which has passed through 
the animal’s body, vigorous discharges from the small end of the tube being 
frequently noticed in the aquarium and attributed by the writer and others 
to this cause. Recent observations, however, have shown that this explanation 
is very far from complete, and that the discharge is an indication of a process 
going on underground, of the greatest importance to the operations and well- 
being of the worm. 
The tube of Pectinaria is constantly growing by additions to its edge of 
grains of sand, most carefully fitted into place by the worm underground. In 
the marked state of commotion produced by the digging process, it would 
clearly be quite impossible for the worm to make the careful selection and 
adjustment of grains suitable to the requirements of each position, which is so 
manifest and marvellous in the finished tube. 
For this purpose quiet and ample working space are needful. These require- 
ments are secured at will by the worm, which ceases its digging operations 
at intervals, and obtains the needful working space in a way hitherto unsus- 
pected. To this end, the sand underground surrounding the edge of the wide 
mouth of the tube must be got rid of. This is effected by a means similar to 
that adopted by dredgers for removing the sand from harbours—namely, by 
suction, After the ground has been broken up by the combs of the worm, and 
the neighbouring sand has been brought within reach and examined by the 
tentacles, the particles not required to be conveyed to the mouth for food are 
carried away by means of a very strong upward current, created within the 
tube by the peristaltic action already mentioned. This causes the sand to 
travel rapidly through the tube, passing between its wall and the dorsal surface 
of the worm, and to be ejected through the small end of the tube, thus forming 
the mounds on the surface of the sand which are generally visible in the 
neighbourhood. 
Tn connection with the underground chamber thus formed, there is usually 
a shaft from the surface a short distance from the tube, and in the aquarium 
the opening of this shaft is frequently visible. 
Hitherto the building organ of the worm appears to have escaped the notice 
of naturalists, but the writer has been more fortunate. It is centrally situated 
slightly below the ventral edge of the peristomium, and consists in its upper 
part of a pair of papillated downwardly directed lobes, which act in connection 
with a lower ‘lip’ formed by the delicate tissues just above the first ventral 
shield. In a specimen suitably prepared a cement-gland, liberally supplied 
with blood-vessels, and somewhat rosette-like in form (about 2 mm. in diameter), 
connected directly with the building organ, is visible by transparency. 
In the light of methods observed and described by the writer with regard 
to other marine tubicolous worms, the above observations have, in his opinion, 
rendered the building operations of Pectinaria (which at one time seemed a 
hopeless problem) easily intelligible. 
: aenetge the act of building has never been seen, the process is doubtless as 
ollows :— 
A working space having been cleared by the method already described, a 
supply of sand is carried by the tentacles to the head of the worm. One portion 
of this sand, to be used for food, is swallowed, and passes through the body of 
the worm; a second portion is carried by the papillz, which form a track, from 
the ventral edge of the peristomium to the building organ, just below. On 
reaching this organ each grain, which is accepted for building purposes, is 
received and held in the hollow between the two lobes. These lobes act as a pair 
of hands in combination with the ‘lip,’ and apply the sand-grain to the free edge 
1913, LL 
