Vermetid Gastropods — Morton 
9 
ments are performed with this fringe which, 
because of the flexibility of the filaments, is 
curved downwards below the margin of the 
shell, and then, more rapidly, the fringe is 
suddenly flexed. Particles engaged by the sep- 
arate filaments travel towards the apices by 
the action of the frontal cilia, embedded in 
a copious secretion of mucus from the axial 
endostyle, which secretion appears to be im- 
mediately induced by the contact stimulus of 
the particles upon the surface of the filament. 
At the same time the lateral cilia, normally 
in rapid motion, become motionless; this is 
of obvious advantage during the "'sweeping 
fringe” type of feeding, in preventing the loss 
of the endostylar mucous secretion by passage 
between the filaments during the beat of the 
lateral cilia. At the tips of the filaments another 
set of cilia, arranged in long apical tufts and 
generally kept inert, now comes vigorously 
into play. The cord of particles collected in 
mucus, which now extends from tip to tip 
around the fringe of filaments, is carried by 
the apical cilia towards the mouth where it 
may either be accepted for ingestion or, as is 
usually the case with experimental carmine 
particles, cast off the filaments and rejected. 
The modifications undergone by the foot 
in Stephopoma can be best appreciated by ref- 
erence to Figure 2b which represents an em- 
bryo recently liberated from the maternal 
pallial cavity and just beginning its brief pe- 
riod of free crawling. In the adult Stephopoma , 
the foot is prolonged in front of the mouth 
into a long, flattened or spatuliform lobe, the 
pre-pedal process. This displays a rather com- 
plicated set of ciliary currents which evidently 
assist in the ingestion of the mucous cord 
from the food groove, or in the rejection of 
loose particles alighting near the mouth, prob- 
ably both. It is formed by the large anterior 
margin of the foot which is squarish, strongly 
ciliated, and very labile in the embryo. In the 
adult, it becomes narrowly constricted from 
the rest of the sole of the foot which remains 
in the form of a broad cushion of whitish, 
ciliated and glandular epithelium, lying, in 
Fig. 2. Diagrams illustrating the structural differ- 
ences between the families Vermetidae and Siliquarii- 
dae. a , Serpulorbis. Section of the head and foot and the 
free crawling embryo; b , Stephopoma. Section of the head 
and foot and the free crawling embryo. In the figure of 
Serpulorbis , the contents of the pallial cavity are dis- 
played through the natural cleft in the female, through 
which the egg capsules are attached to the shell. In 
Stephopoma, the pallial cavity has been opened by the 
removal of a portion of its right wall, to display the 
tips of some of the ctenidial filaments in end view. 
The arrows indicate the directions of the principal 
ciliary currents. In the embryos note the spirally coiled 
embryonic shell, and compare with the figures of the 
adults, to see the modifications involved in the develop- 
ment of the head and foot. 
AD, Adult portion of the shell added to the nuclear 
shell in Serpulorbis; CE T, cephalic tentacle; CPS, egg 
capsules; f g, food groove in Stephopoma; fil, gill 
filaments; F s, sole of the foot; f tr, food tract in 
Serpulorbis; hy g, hypobranchial gland; OP, operculum; 
PA, mantle; PE G, pedal gland; PE T, pedal tentacle; 
p ped, pre-pedal process in Stephopoma; PR, proboscis; 
rej, rejectory tract of foot; rm, rectum with faecal 
pellets; sh, shell. 
