POLYCH.ETA FROM THE N.E. PACIFIC, 981 
used as organs of progression, pushing the animal along. The 
worms can thus move with some rapidity, and they can also turn 
within the tube and even pass each other. When at rest they 
generally lie with the long tentacles projecting from an aperture 
evidently questing for food. All the inhabitants of the tube may 
not be able to obtain such advantageous situations, but from 
their activity within the tube it is evident that a fr equent inter- 
change of position does take place. The worms do not all lie the 
same way, so it is difficult to see how a constant and sufficient 
circulation of water can be maintained through the whole tube. 
Probably at times the animal is entirely quiescent and the 
respiratory current interrupted. In all the animals I observed, 
the action of the cilia in the dorsal groove and of the notopodia 
of the median region is responsible for a current running poste- 
riorly, which supplies not only oxygen but also food, as in the 
other Chetopterids. This action is sometimes vigorously supple- 
mented by the undulatory movements of the abdomen. This 
energetic action—a phenomenon often observed, too, in Cheto- 
pterus—is possibly necessary for removing objectionable particles 
from the neighbourhood of the body. hn P. anglica and to a 
less degree in P. prolifica, 1t may be seen, however, that the 
circulation of water is not always thorough, for large sections of 
the tube behind worms are blocked by fecal masses, and this 
may eventually necessitate the abandonment of the old parts and 
extension of the colony. 
I have not observed any individuals bearing genital products, 
but this is probably due to insufficient examinations and I should 
not like to suggest that asexual generation has supplanted the 
sexual method. Isolated individuals (like those of Chetopterus) 
are not able to manufacture fresh tubes in spite of copious secretion 
of mucus, and new colonies must be formed in the first place by 
a single individual developed from a fertilised egg, though this, 
by fragmentation, gives rise to all the inhabitants of the Rcolony 
Claparéde made the interesting observation that, in P. socialis, all 
the worms in a bundle of tubes developed genital products of the 
same sex, indicating that they were all derived from a single 
sexually produced embryo. 
Some Ports IN THE MoRPHOLOGY OF THE CH&TOPTERIDE. 
Variation in Form of the Notopodia.— Behind the anterior 
region of the body both notopodium and neuropodium are 
present in the parapodium. In nearly all cases the neuropodium 
is stable and retains its character as a double uncinigerous ridge. 
In Mesochetopterus, where the first neuropodium of the median 
region is single, there is a slight modification, and in Cheetopterus 
the neuropodia of opposite sides in the median region are fused 
to form a sucker. 
The notopodium, on the other hand, is very variable, and it 
