208 HIGHWATER MARK. 



running of the dark points is in the opposite direc- 

 tion. For hours and hours, nay even for days, this 

 incessant chase goes on, never slackened, never inter- 

 mitted, until the progress of decomposition has de- 

 stroyed the cohesion of the parts ; and even then the 

 movement may be discerned lingering in the dissolv- 

 ing fragments. 



You will not, however, have acquired an adequate 

 idea of the nature of this curious phenomenon, till 

 you have made an examination, your judgment 

 fortified by the facts you have just observed, of 

 the living and uninjured tissue. Returning to the 

 Mussel, look carefully over one of the untouched leaves 

 of the gills with a good pocket-lens, and then you will 

 see that there is but one thread. The entire gill-leaf is 

 formed out of a single thread, folded to and fro upon 

 itself, with some hundreds of turns through the whole 

 length, and that the running points maintain in every 

 part the same law of motion , their course being up 

 one side of the thread and down the other throughout. 



But these mysterious black points, what are they? 

 and what the nature of this strange race, which those 

 tiny chasseurs maintain with so indomitable an energy, 

 every one striving, and with success too, to be in at 

 the death ? It is very hard to persuade one's-self that 

 they are nothing at all ; and when, after a quarter of 

 an hour's gaze at the untiring objects, your sage micro- 

 scopic Mentor tells you that they are no objects at all, 

 you look up to see if he is laughing at you. But no ! 

 the sage is as sober as a judge ; and you demand an 



