SEA-URCHINS AND SEA-CUCUMBERS. 277 



&So I brought it home, and now produce it as the text of 



our conversazione. 



Every part is a wonder; but we must examine each in 

 •order. Take the spines first. 



As, using this triple lens, we examine these organs 

 • on the animal crawling at ease over the bottom of a 

 ■saucer of sea- water, we see that each is a taper pillar, 



rounded at the summit, and swelling at the base, where 

 -it seems to be inserted into a fleshy pedestal, on which 



it freely moves, bending downward in all directions, and 



 describing a circle with its point, of which the base is 

 the centre. Each spine is for the greater portion of its 

 length of a delicate pea-green hue, but the terminal part 



 is of a fine lilac or pale purple. The whole surface 

 appears to be fluted, like an Ionic column, but this is an 

 illusion, as you will see presently. 



I now detach one of the spines, cutting it off with fine- 

 pointed scissors as near the base as I can reach. I put it 

 with as little delay as possible into the live-box, and 

 examine it with a high power, say 600 diameters. Look 

 -at it. You see the ciliary currents very distinctly; and 

 t if you move the stage so as to bring the basal portion 

 .into view, you may discern even the cilia themselves, 

 very numerous and short, quivering with a rapid move- 

 ment. The currents are not longitudinal, but transverse, 

 and somewhat peculiar. The floating atoms which come 

 within their vortex are drawn in at right angles to the 

 axis of the spine, and are presently hurled away in the 

 same plane; forming a circle, whose plane is perpendicular 

 to the direction of the spine. The surface upon which 

 these cilia are set is a transparent gelatinous skin, of 

 extreme tenuity, stretched tightly over the solid portion, 

 which it completely covers, and studded with minute 

 oval orange-coloured grains. 



The substance of which the spines are composed is best 

 seen by crushing a few of these organs into fragments. 



