310 



EVENINGS AT THE MICROSCOPE. 



You have doubtless observed, while gazing on the ani- 

 mal, a peculiar glittering appearance along its sides, 

 mingled in certain lights with brilliant rainbow-reflections. 

 Now let us take an opportunity, when it approaches the 

 side of the glass, to examine this appearance with a lens. 

 The globe, you see, is marked by longitudinal bands, eight 

 in number, set at equal distances, and ranging like meri- 

 dians, except that they do not quite reach to either pole. 

 These bands are the seats of the motile organs, which are 

 highly curious, and in some sort peculiar. 



Each^band is of considerable width in the middle, but 

 becomes narrower towards the extremities. It carries a 



number usually from twenty to thirty of flat thin mem- 

 branous fins, set at regular distances, one above the other, 

 which may be considered as single horizontal rows of cilia, 

 agglutinated together into flat plates. Each plate has a 

 rapid movement up and down, from the line of its inser- 

 tion into the band, as from a hinge, and thus striking the 

 water downwards, like a paddle. The whole band may be 

 likened to the paddle-wheel of a steamer, except that the 



