386 Prof. J. Reid on the Anatomy and 



lower and upper edges^ but more deeply in the former than the lat- 

 ter. From this aperture a hair-like prolongation (fig. 2 d), about 

 the length of the cell^, and slightly curved^ projects. The interior 

 of the process is filled with a fibrous contractile substance which 

 moves this hair-like prolongation. Its movements occur at irre- 

 gular, occasionally very short intervals, and it sweeps downwards 

 over all the posterior surface of the polypidom within its reach. It 

 then turns back upon its former track, ascending upwards until 

 it reaches again the outer edge of that part of the polypidom 

 lying above the process to which it is attached ; it now descends in 

 the opposite direction over the outer part of the polypidom, and 

 places itself along the outer edge of that portion of the polypidom 

 lying below it. From this it re-ascends in the course just de- 

 scribed. The extent of these movements is increased by the pre- 

 sence of the notches in the edges of the aperture through which 

 the hair-like prolongation passes. These movements are perfectly 

 independent of the polype and continue for days after its death. 

 The upper and outer edge of the polype-cell is prolonged into a 

 process (fig. 1 a, and fig. 2 c) mucronated at its external and up- 

 per angle. This process is hollow and is filled with a pale fibrous 

 contractile substance, which I have frequently seen become elon- 

 gated and rise in the form of a short conical eminence above the 

 upper edge of the process, and then after a while it contracted 

 suddenly and retired within the process. This process was in 

 some cells metamorphosed into a strong spine (fig. 1 h), and in 

 such cases three spines were attached to the external angle of the 

 cell instead of two the normal number. It has an affinity with 

 the tooth-like process of Cellularia scruposa, as both contain a 

 similar contractile substance. Placed between the bases of the 

 above two processes and overlapping the latter, is a rounded small 

 cavity with a distinct circular aperture (PI. XII. fig. 2 a). In some 

 cells all these three appendices are wanting ; in others only one 

 of the two former is present. The polype protrudes itself through 

 a small aperture directed outwards and upwards, placed at the 

 upper end of the cell and towards its outer edge, and immediately 

 in front of the process bearing the hair-like prolongation (fig. 3 a). 

 This aperture is crossed anteriorly by a pretty strong rim which 

 forms the upper edge of the anterior surface of the cell, and pos- 

 teriorly by the still stronger rim forming the upper edge of the 

 posterior surface of the cell. Below this aperture there is a 

 considerable portion of the anterior wall of the cell formed by a 

 transparent membrane, and bounded by a thick edge, constitu- 

 ting the large oval opening in the anterior wall of the cell in dead 

 or dried specimens. In the greater number of cells this space is 

 crossed by bars of calcareous matter, growing from its inner 

 margin by one stem which generally divides dichotomously into 



