OF TUBULAR AND CELLULAR POLYPI, AND OP ASCIDI^. 377 



moving slowly about. The ova that grew naked among the scattered arms had a 

 central opake portion, more distinguished from the surrounding albumen than in those 

 of the ovaries just described. A stream of particles flowed through the short pedicle 

 of the ova, alternately into and out of their central part ; which swelled with the in- 

 ward flow, and shrunk with the returning one ; the flux and reflUx were about two 

 minutes each. The alternate current was seen in the axis of the cell, but the other 

 parts of the line were too opake to show it : there appeared to be none in the trans- 

 parent albumen, nor in the arms. 



The examples given exhibit the circulating fluid of the Sertularioe under a variety 

 of circumstances. It appears from them to be the great agent in absorption, and to 

 perform a prominent part in the obscure processes of growth ; and its flow into the 

 stomach of the polypi seems to indicate that in the very simple structure of this family 

 it acts also as a solvent of the food. 



The particles carried by it present an analogy to those of the blood in the higher 

 animals on one side, and of the sap of vegetables on the other. Some of them appear 

 to be derived from the digested food, and others from the melting down of parts ab- 

 sorbed ; but it would be highly interesting to ascertain distinctly how they are pro- 

 duced, and what is the office they perform, as well as the true character of their re- 

 markable activity and seemingly spontaneous motions ; for the hypothesis of their 

 individual vitality is too startling to be adopted without good evidence. 



I could not satisfy myself as to the immediate cause of the currents. Preceded as 

 they usually are by agitation of the particles, and in the absence of all appearance of 

 muscular contraction of the soft matter in the tubes, the explanation of this question 

 may perhaps depend on that of the former. The alternate swelling and shrinking of 

 the pulp supposes either a filtration of water through the parietes of the tube, or a 

 current of animal fluid, which I could not perceive, flowing between the tube and the 

 pulp in a direction opposite to that in the axis ; for it is evident that (in Campanularia, 

 at least, and the same may be inferred throughout,) there is no interruption at the 

 seeming joints to the continuity of the shell. 



Along the arms of the Sertularioe there are at intervals short projections like blunt 

 hairs, single or in tufts, and generally more numerous towards the ends; and it 

 seems to be by their means that the polypi attach with a touch, or release at will, 

 substances that drift within their reach. In Coryne there is a similar provision on a 

 knob at the end of the arms. I have never seen in either the least appearance of ciliae, 

 nor any of those currents in the water near the polypi which are so conspicuously 

 produced by other tribes of zoophytes. Must we infer that this family is furnished 

 with no means of respiration ? or (adopting one of the suppositions suggested above) 

 may the exposure of the soft matter to water, passing in and out through pores in the 

 shell, supply its place ? 



In the processes of growth, the shell must evidently be thickened at some places. 



