6 J. SPENCER ON ZOOTHAMNIUM ARBUSCULA. 



•without the peg, and was furnished round the widest part with an 

 undulating ribhon or membrane of sarcode broken at the edges, 

 but not quite developed into cilia, parts of which moved slowly 

 like little tongues of flame, some waving in one direction, some in 

 another. In the course of five minutes this membrane became 

 completely divided into cilia, which commenced the characteristic 

 movements of the cilia of the vorticella, and in a few seconds 

 acquired rapid movement, when the creature became disconnected 

 from the parent stem and swam out of the field of view. When I 

 first observed it on the Thursday morning it had already acquired 

 the shape shown in Fig. 7, and when it was detached it was shaped 

 as in Fig. 9. I continued watching the colony, and saw that near 

 the point of junction of another spheroid with the stem a slight 

 movement of a mere thread of sarcode projecting from the 

 periphery. This became gradually broader, forming a thin un- 

 dulating ribbon, attached by its edge to the ball, and insensibly 

 rising until it occupied the position shown in Fig. 6 ; then the ball 

 very gradually altered in shape until it resembled two conoidal 

 bodies united at their bases, as shown in side and front view at 

 this stage in Figs. 7 and 8. In a few seconds it assumed the 

 shape indicated in Fig. 9, with swiftly vibrating cilia, and detached 

 itself and swam away. I saw another spheroid pass through all 

 these changes on the Thursday evening, and saw the last of the 

 nine do so the next day. 



While the alterations in the reproductive zooids were progress- 

 ing, the ordinary campanulate zooids gradually disappeared, and 

 when the last reproductive zooid swam away there were but a few 

 of the ordinary zooids left at the ends of the twigs, but the 

 muscular system was contracting as vigorously as ever. I saw the 

 objects I have described in all positions, and the nature of the 

 changes was very distinctly visible. From the time I began to 

 observe each of the zooids, in which I saw the whole of the 

 changes from a spheroid attached to the colony to a freely 

 swimming bell, I did not take my eye from the microscope, the 

 time occupied in each case being from 30 to 35 minutes. 



