On the behaviour of Sabella

The water currents which Sabella ( = Spirographis) spallanzanii and S. pavonina drive through their tubes vary with time according to definite and characteristic patterns. These are described in detail, and the bearing of the results on the general physiology of the worms is considered. In either species, the tube consists of a stiff stem and a more flexible root, and is open at both ends. The opening of the stem (anterior opening) is always well above the substratum. That of the root (posterior opening) was found to be above the surface of the substratum in S. spallazanii but embedded in the mud in S. pavonina. This means that the tube can easily be irrigated in either direction in S. spallanzanii but tailwards only in S. pavonina. The water currents were recorded by cutting away the root and connecting the posterior end of the stem to a recording apparatus, which opposed very little resistance to the water move­ments. The worms remained healthy and active for many days on the apparatus. Both species irrigate their tubes vigorously whether the crown is expanded or withdrawn. In S. spallanzanii, pauses are brief and rare; the direction and velocity of irrigation often change and certain characteristic behaviour patterns are constantly reproduced. In S. pavonina, there may be pauses of over an hour’s duration, and irrigation is tailward only. The fact that the former species irrigates in either direction and the latter in one direction only is clearly correlated with the difference in form of their tubes. As the worms were studied under practically identical mechanical conditions, the behaviour difference is inherent. Decapitation (removal of crown, collar and part or all of the thorax) has very little effect on the irrigation behaviour of either species. Closure of the circulation (so that the worms circulate a small volume only of non-aerated water) causes a reversible inhibition of irrigation in S. spallanzanii. A worm may still be very active, even though its crown is withdrawn into its tube. The behaviour of the worms when the crown is withdrawn was studied by transferring them to glass tubes, and closing the ends with caps which permitted a through circulation of water but prevented the extrusion of the crown. Some of the worms were adversely affected by the transfer, and failed to irrigate the glass tubes. In those which irrigated the glass tubes in a normal way, forced withdrawal failed to stop the circulation of the blood or the collection of carmine particles by the crown, even if the caps were left on for over 24 hr. The suggestion is made that under natural conditions the worms may sometimes feed from the irrigation current when the crown is withdrawn. The respiratory significance of the crown and the function of chlorocruorin are briefly discussed.