THE HEAKT. 303 



which the cilia make : the cilia themselves being hairs, 

 so fine as to be defined only with high powers. Occa- 

 sionally we see one or other of the ovals suddenly cease 

 its movement, while the rest go on ; and now and then 

 the whole are arrested simultaneously, and presently 

 all start off again together, with a very pleasing effect, 

 as if we were looking at the wheels of a very perfect 

 and complex piece of machinery. These phenomena 

 appear to indicate that the movements are under the 

 control of the animal's will, capable of being suspended 

 or continued, wholly, or in any degree, at pleasure ; 

 which is not the case in the higher animals ; our own 

 respiratory movement, for example, as well as the pulsa- 

 tions of the heart, going on without the concurrence of 

 our will, and even without our consciousness. 



The action of the heart in these transparent* creatures 

 is equally visible. Below the muslin curtain with its 

 living chambers, down at the very bottom of the body- 

 cavity, there is a transparent sac of membrane, which 

 takes the appearance of a long bag, pointed at each end, 

 but not closed, and strangely twisted on its long axis, 

 so as to make three turns. This is the heart ; and 

 within it are seen many colourless globules, floating 

 freely in a clear fluid, which answers to the blood. 

 This circulates throughout the system in the following 

 manner : We see a spasmodic contraction at one end 



