42 



Having thus succeeded in seeing the continuous entrance and exit of 

 the surrounding fluid, the great saccular cavity was next examined. 

 This was done by carefully opening the sponge, from the entrance of 

 the sac to its base, with a pair of fine scissors, cutting through its 

 compressed edges. The halves thus produced were mounted for 

 examination in a closed cell as before, with the inner surface towards 

 the eye. The sponge was now seen to be composed of angular cells, 

 constructed of triradiate, calcareous spiculae, and packed together 

 like the cells of a honeycomb. They are of the same diameter 

 downwards for the length of about half their own diameter, and then 

 terminate in a perforated diaphragm, the circular mouth of which is 

 of about half the diameter of the cell above it. Beneath this 

 diaphragm an elongated cavity or cell extends, and opens on the 

 outer surface of the sponge ; the whole length of the cell, from the 

 inner edge of the diaphragm to its termination near the outer surface, 

 being closely studded with tesselated, nucleated, cellular structure. 

 Within the diaphragm, and between the inner termination of the 

 incurrent orifices, are situated the cilia, which are of excessive 

 tenuity, and comparatively of considerable length. Upon focussing 

 the diaphragm, the cilia may be seen in rapid motion within the 

 area of tlje circular orifice, many of them being tipped with a minute 

 portion of a gelatinous or of fecal matter, and thewhole of them 

 continually oscillate in a plane parallel to the edge of the diaphragm, 

 occasioning a continual current through its orifice. 



Although both the presence and action of the cilia were very 

 clearly shown by this mode of examination, still neither the extent 

 of surface covered by them, nor their insertion, could be determined. 

 By dividing, however, one of these cells through its whole length, 

 which, after many trials and failures, was at last effected, portions of 

 these, examined in the same manner as in the preceding instances, 

 exhibited ciliary action ; and as the vital energy decreased and their 

 motions became languid, one cilium in particular was observed, which 

 continued for nearly half an hour to wave gently backward towards 

 the outer surface of the sponge, and then rapidly forward towards the 

 mouth of the diaphragm. Many other cilia were observed, but none 

 so distinctly exhibited their peculiar action as this ; and it was found 

 that although it may be highly probable that the cilia are based upon, 

 or spring from among, the tessellated cells, it was not possible to 

 ascertain the fact precisely ; but sufficient was shown not only to 

 prove the existence of ciliary action in the sponge, but also, by the 

 peculiar motion just described, to account for the flow of the current 

 in one direction. 



