GILLS OF MUSSEL. 207 



that the slightest touch tears them into strips, the 

 rent invariably proceeding directly across their short 

 diameter. 



But let us with sharp scissors cut out a portion of 

 one of these leaves, and, laying it on the lower glass 

 of what microscopists call a live-box, cover it with a 

 drop of sea-water, which we then flatten by putting 

 on the glass cover. Now to the stage of the micro- 

 scope with it, and put on in succession magnifying 

 powers varying from 50 to 250 or 300 diameters. 

 The whole field of view is a scene of the busiest 

 activity : movements of the most exquisite regularity 

 and precision, and of unceasing activity, are going on 

 in every part. A most attractive spectacle is before 

 us, which evokes our delight not less than our wonder. 



We see a great number of threads of great delicacy 

 and flexibility, with a tendency to a parallel arrange- 

 ment ; but forming bundles of varying breadth, lying 

 across each other in various directions. Each frag- 

 ment is composed of more or fewer of the elementary 

 threads, laid side by side in close contact, or almost 

 contact. Along these threads we see a very peculiar 

 series of movements. Under the higher powers of 

 the microscope, these are very interesting. Fixing 

 our attention on one thread, and watching it, we dis- 

 cern a multitude of black points running along the 

 thread with a moderately rapid, equable course, all 

 chasing each other with ceaseless perseverance. This 

 is on one side of the thread ; but on the other side a 

 phenomenon exactly similar is seen, only that the 



