Transport of food through the alimentary canals of aquatic annelids.

DURING an investigation of the blood system in polychaetes of the families Serpulidae and Sabellidae the musculature of the alimentary canal has been studied. In the following species the only muscle coat, which consists of fibres lying transverse to the main axis, lies outside the blood sinus which envelops the canal: Serpula vermicularis L., Hydroides norvegica (Gunnerus), Vermiliopsis infundibulum (Philippi), Pomatoceros triqueter L., Protula intestinum (Lamarck), Apomatus ampulliferus Philippi, Salmacina incrustans Claparede, Spirorbis militaris (Claparede), 5. corrugatus (Montagu), Potamilla sp. and Dasychone lucullana (Delle Chiaje). In Sabella spallanzanii (Viviani) (Ewer, 1946) there is another layer of circular muscles between the sinus and the gut epithelium. This inner muscle coat has also been seen by Evenkamp (1931) in Laonome kroyeri and Euchone papillosa, and Dr. A. Stock (personal communication) has found it in Sabella pavonina. In the rest of the literature on serpulids and sabellids the only circular muscle coat recorded is the one situated in the outer wall of the blood sinus. It has been known for a long time (Claparede, 1873) that these uscles contract antiperistaltically, moving the blood forwards in the sinus. In the smaller species it can be seen that the antiperistaltic contraction waves not only constrict the sinus but frequently may also slightly constrict the lumen of the gut. When a contraction wave passes a food bolus the latter is moved for a short distance towards the mouth, but after the passage of the wave quickly returns to its original position. Stephenson (1913) in his well-known paper 'On Intestinal Respiration in Annelids' has shown that antiperistaltic contraction of the gut musculature is not a peculiarity of serpulids and sabellids, but, with very few exceptions, is found in all the many aquatic annelids he examined, whether or not they possess a gut sinus. Where a sinus is absent he postulated that the antiperistaltic mode of contraction of the gut musculature has been retained during evolution from ancestors possessing a sinus. Hence, in aquatic annelids in general, the contents of the alimentary canal are not moved along by peristaltic contractions of its wall as they are in other animals, but the activity of the musculature actually tends to hinder their movement towards the anus. The direction of the contraction waves in the extra muscle coat of Sabella, Laonome, and Euchone is not known.