SOME POINTS IN THE ANATOMY OF POLYCILETA. 271 



the end of the body. These tubular fibres have been well 

 described by Claparede 1 as they occur in Spirographis Spal- 

 lanzanii. He found several transverse connecting branches be- 

 tween the two tubes in the thoracic region immediately behind 

 the union of the oesophageal commissures, and he traced the tubes 

 into these commissures, where each divided into two branches. 

 These branches passed forwards into the cerebral ganglion, 

 where they ramified into thinner and thinner branches, but the 

 ultimate terminations Claparede could not discover. 



I have endeavoured to trace the anterior extremities of the 

 tubes in Sabella penicillus. I found a transverse connect- 

 ing tube in the first transverse commissure, like those described 

 by Claparede, but could not find more than one, and it is 

 noticeable that while Claparede mentions a number of these 

 anastomoses in the text he figures only one. I found that the 

 tube, much diminished in diameter, passed up the oesophageal 

 commissure, but could not discover that it branched. In my 

 sections it seems to become smaller and smaller, and simply 

 end blindly. 



In Sabella the mass of ganglion cells representing the cere- 

 bral ganglion is situated on each side of the oesophagus, and 

 below it is the fibrous oesophageal commissure, which is con- 

 tinued by an arch above the oesophagus into its fellow of the 

 opposite side. The tubular fibre ends below this mass of 

 cerebral ganglion cells, and, as far as I can see, sends no 

 branches towards the mass, nor could I see any trace of a 

 connection between the end of the tube and any ganglion 

 cells. 



Although these structures are spoken of as tubes, they are 

 not actually empty. Their interior in the sections is par- 

 tially filled by a transparent gelatinous-looking mass, which 

 for the most part does not stain ; but there are lines in the 

 mass which are stained, and which somewhat resemble a net- 

 work of fibres. In my opinion these stained lines are due to 

 the unequal coagulation of the gelatinous mass, which during 



1 " Structure des Annelides Sedentaires," ' Mem. Soc. de Pliys. de Geneve,' 

 torn. xxii. 



