OP TUBULAR AND CELLULAR POLYPI, AND OF ASCIDI^. 369 



others I have not seen ; but Plumularia, Sertularia, and Campanularia belong to one 

 very beautiful natural family, for which the old name of Sertularice may perhaps be 

 well retained, and these are the subject of the observations under the present head. 

 The specimens figured include some principal variations in the form and position of 

 the cells. 



Sertularia pluma, Plate VIII. fig. 2. (Ellis, pi. vii. b B. Plumularia pluma, Lamarck), 

 was found at Dover, October 1832, on the ropes oi Fucus siliquosus. It consisted of 

 a minute horny tube, creeping along and round the Fucus with frequent anastomosis, 

 (a usual property of the Sertularice^ and sending out offsets at short intervals. These 

 had each a main stem, feathered with jointed branches directed to each side alter- 

 nately in close succession : every joint was elaborately formed of thin transparent shell, 

 of ^^which one part continued the branch, and the rest formed a cell for a polypus ; 

 all the cells on a side branch taking one direction. Each plume might comprise 

 from 400 to 500 polypi. It was neglected to be drawn till the polypi were shrunk : 

 when living, their arms spread widely, their body scarcely projecting beyond the 

 edge of the shell. 



All the polypi were connected together by a soft matter, of a pulpy or finely 

 granulated appearance, which was a continuation of their substance, and extended 

 throughout the interior of the branches, the stem, and the creeping tube or root. 

 When a magnifying power of 100, and still more clearly when one of 300, was used, 

 a current of particles, various in size and of irregular form, was observed running 

 along the axis of this soft matter. It flowed in one channel, alternately backwards 

 and forwards, through the main stem and lateral branches of a plume, and through 

 the root as far as the opacity admitted of its being traced : sometimes it was seen 

 to continue into the cells. The stream was throughout in one direction at one time : 

 it might be compared to the running of sand in an hour-glass, and was sometimes so 

 rapid in mid-tide that the particles were hardly distinguishable ; but it became much 

 slower when near the change. Sometimes it returned almost without a pause ; but 

 at other times it was quiet for a while, or the particles took a confused whirling 

 motion for a few seconds, the current afterwards appearing to set the stronger for 

 this suspension. The whirling or starting motion took place sometimes at one some- 

 times at another part of the stem and branches during the intervals of the currents. 

 Five ebbs and five flows occupied fifteen minutes and a half, the same average time 

 being spent in the ebb as in the flow. The longest continued stream was two minutes 

 and a quarter ; the longest suspension, half a minute. 



When the connexion of a plume with the root was interrupted by bending its stem, 

 the stream running down the middle was observed to continue its flow up one of , the 

 lower and stronger lateral branches, and then to return down that branch and up 

 the main stem, the course of the current in most of the other side branches being 

 still the same as in the middle one. 



On a stem being cut off below the commencement of the side branches, a few 



