352 EVENINGS AT THE MICROSCOPE. 



metry. By means of the high magnifying power which I 

 have now applied, each of these pinnae is seen to be 

 roughened with whorls of knobs, which are accumulations 

 of cnidsB, analogous to those which we lately demonstrated 

 in the tentacle of Laomedea. 



In the midst of the area surrounded by the petal-like 

 tentacles, a narrow slit opens into the stomach. This 

 organ is a flat sac, resembling an empty pillow-case hang- 

 ing down- in the centre of the column, and open at the 

 lower end. From this end, which does not extend to 

 more than one-sixth of the depth of the cavity, three 

 threads, much twisted and irregularly thickened, spring 

 off at each side and arch downwards, for a short distance. 

 These are the reproductive organs, which fringe the free 

 edges of as many delicate membranes which run up as 

 perpendicular partitions between the stomach and outer 

 wall, uniting with both, and thus dividing the space sur- 

 rounding the stomach into chambers open at the bottom. 

 There are eight of these septa (as the partitions are 

 called), but one on each side is destitute of the fringing 

 twisted thread. 



The whole surface of the interior — the walls, the 

 stomach, and the septa — is clothed with fine vibratile 

 cilia, by the action of which constant currents are main- 

 tained in the water, which bathes every part of the cavity, 

 freely entering at the mouth. We can distinctly trace 

 these ciliary currents hurling along with irregular energy 

 the products of digestion, in the form of translucent 

 granules, especially along the edges of the septa. 



Though the substance of the polype is soft and flexible, 

 it contains solid elements. Just below the expansion of 

 the tentacular blossom, we see imbedded in the skin a 

 vast mass of calcareous needle-like bodies called spicula. 

 Individually, these are very minute, and their form is 

 swollen in the middle, and taper at each extremity, the 

 whole roughened with projecting knots. Collectively, they 



