226 EVENINGS AT THE MICROSCOPE. 



points, there is a round opening, for an object which we 

 shall see presently. Such is the shell, or lorica, as it is 

 technically called, which is of a rather stiff, elastic consist- 

 ence, of a horny (chitinous) texture, and of the most 

 glassy transparency, permitting us to trace every vessel, 

 every organ, and every function of the animal within the 

 shell with perfect distinctness. The little creature is of 

 unwonted dimensions in its class, for it is one thirty-sixth 

 of an inch in length. Hence, to the unassisted eye, it is 

 just visible as a white speck moving in the water, while a 

 pocket lens reveals its beautiful form. 



Within this translucent shell you see a confused mass 

 of moving viscera, a multitude of irregular sacs and bands, 

 lying over each other, whose crowding, changing, and 

 vanishing lines distract the attention, and prevent you 

 from making out anything definitely. But a waved out- 

 line of limpid flesh is protruding from the rim of the shell ; 

 and now, having reached beyond the level of the spine- 

 points, it rapidly unfolds into three broad, fiattish lobes ; 

 and in an instant each of the two lateral ones is crowned 

 by a wheel of dark points in rapid horizontal revolution. 

 Is not this a charming sight ? Kound and round go the 

 wheels, forming two perfect crowns, which rotate with 

 uninterrupted and unceasing course, smooth and regular, 

 which we can compare with nothing else than the crown- 

 wheel of a watch, if allowed to run down. 



Now these are examples of ciliary action. Though at 

 first it is almost impossible to persuade oneself that there 

 is not an actual rotation of parts, yet this is only an illu- 

 sion, as I have already explained. The waves alone move, 

 the cilia themselves retaining their position unchanged, 

 except that they alternately bend and erect themselves. 

 It may assist your idea of this motion to advert to a field 

 of com over which a smart breeze is blowing. You see 

 that waves chase each other across the field ; but your 

 reason, indeed your observation, tells you, that this appear- 



