OP TUBULAR AND CELLULAR POLYPI, AND OF ASCIDIiE. 373 



The young branch, Plate IX., furnished an instance of the progressive production 

 of a polypus ; for having been drawn (August 19, 1833,) on account of the singular 

 form of the cell h, the sprout c was found to have lengthened during the tracing, 

 and this led me to watch its growth at intervals during that and the following day. 

 About five hours were spent in the completion of the footstalk, and twenty-seven 

 more in that of a cell and its polypus. 



The branch sprang from a creeping tube that had been recently broken at a little 

 distance beyond. This, like the pruning of a tree, may have accelerated the growth ; 

 and from the same cause as was supposed, the internal currents were very irregular. 

 Dancing of particles sometimes took place along the whole stem, sometimes at parts 

 of it only. The set of the stream was sometimes up or down a h and c altogether, 

 sometimes out of a into c, or the contrary. Before a current in the stem became 

 strong, some particles would for a while appear to struggle on against it. The sprout c, 

 which looked like a continuation of the stem, was at first quite full of soft matter, 

 and the motion of the currents in it was inconsiderable; but they increased so as 

 soon to become greater by far there than in any other place, and its soft part was 

 then dilated and contracted alternately, except at its end, which was always full. 

 The time of the stream's running into c was, on an average of seven alternations, six 

 minutes ; of the reflux four minutes. The longest time of the former was eight mi- 

 nutes and a half, the shortest of the latter two minutes. In about two hours the 

 sprout had assumed the appearance c 2. Particles of larger size were now seen, 

 maintaining a continual circulation within, except that all was still for a short time 

 when the pulp was most shrunk : when it was dilated they had great agitation. 

 Their flow was always downwards along the axis, and upwards along the sides of a 

 defined cavity, being in a direction opposite to that observed in the polypus of Tuhu- 

 laria ; and the manner of the flow, and the abundance of fluid, more resembled the 

 circulation of Chara than anything I had before seen in Sertularia ; but still the 

 dancing motion distinguished them. Some of the particles were nearly round, and 

 transparent, other larger ones seemed like masses of the pulp brought into circu- 

 lation. 



The part of the branch towards the end was more opake than the rest : slight 

 currents were occasionally seen in the axis there at long intervals ; and the outer 

 portion of this part, which was in the act of growth, had not a granulated ap- 

 pearance, but was marked with radiating lines nearly parallel to each other in front, 

 and more diverging on the sides, so as to make always a considerable angle with the 

 surface ; and among them no current or motion was seen. 



In six hours more the branch had the shape of c 3, the rudiments of a cell/appearing 

 at the end : its commencement was about three hours previously. The peculiar 

 circulation down the axis and up the sides was now only during the latter part of 

 the influx ; the dilatations were lessened, and a part of the shell at d was never 

 filled ; a separate agitation had begun to show itself at e, and a faint one at/. 



MDCCCXXXIV. 3 c 



