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A Case of Regeneration in Polychate Worms. 

 By Arnold T. Watson, F.L.S. 



(Communicated by C. S. Sherrington, F.R.S. Received October 23, 1905, — Read 



January 18, 1906.) 



The facts recorded in the following note were ascertained in the course of my 

 observations made upon a marine rock-boring polychaete worm found at Tenby 

 in the spring of the present year. This worm, a species of Potamilla, is living 

 in limestone rock, in which another species of the same genus, Potamilla 

 reniformis, is. also burrowing. It differs from the latter in various particulars, 

 amongst which may be noted the absence of eyes on the branchial filaments, 

 the colour of the blood (which is red instead of being sometimes green), the 

 form of the setae, and the character of the external tube, which is largely 

 covered, especially at the tip, with minute pieces of shell attached edgewise, 

 imparting to it a white, rugged appearance, somewhat similar to that of the 

 tube of Owenia. The worm is sometimes as much as 3^ inches long, and is 

 seldom extracted entire from the rock, fragments only, of varying length, 

 usually being obtained. 



It occurred to me that this material might be utilised for the study of the 

 regeneration of the lost parts, and my experiments in that direction succeeded 

 beyond my expectations. Not only did the fragments renew these parts (both 

 anterior and posterior) but they demonstrated the existence of a power to 

 economise labour in this respect, by changing the arrangement of certain of 

 the old parts, so as to complete the model of the original animal. 



The body of the worm in question consists of a large number of segments, 

 all of which, with the exception of those at the two extremities, are endowed 

 with a set of hooks (uncini) and bristles (setae) on either side, and it is one of 

 the characteristics of the Sabellidae, the family to which this worm belongs, 

 that the character and arrangement of these appendages in the anterior or 

 thoracic portion differs from that in the posterior or abdominal part. The 

 setae in the former are situated dorsally and the uncini ventrally, whilst in 

 the abdominal portion the uncini are dorsal and the setae ventral. This 

 arrangement, besides enabling the worm to rotate on its long axis in either 

 direction at will, also facilitates the bringing of its thoracic ventral glandular 

 plates and collar-lobes into contact with the inner surface and top of the 

 tube, and is probably connected with the tube-forming habits of the worm. 

 Some of the fragments which I have had under observation were without 

 head and thorax, and consisted of abdominal segments only, the setae and 

 uncini consequently being ventral and dorsal respectively, from end to end. 



