226 EVENINGS AT THE MICROSCOPE. 



two bottom 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 consistence, 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 

 outline 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, flattish 

 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 sicrht 1 Round 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 corn 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- 



