VIII.] STRUCTURE OF CONTRACTILE TISSUES. 81 



b. The free surface is densely studded with 

 cilia. The cilia seen in profile appear to 

 form a row, but when a cell is seen in face, 

 they are foreshortened into mere dots and 

 are seen to be spread over the whole surface. 



c. The nucleus is not very obvious but may, 

 with its nucleolus, be made out; the cell- 

 substance is somewhat granular but has a 

 non-granular, hyaline border just below the 

 cilia, 



2. Cut out a small piece of the same membrane in 

 a recently killed frog, place it on a slide, from a 

 portion of it scrape off the epithelium and tease 

 out the scrapings in normal salt solution; with 

 this mount the unteased portion of membrane 

 putting a fragment of paper underneath the 

 cover-slip. Note 



a. In the unteased portion the shimmering ap- 

 pearance caused by the movements of the 

 cilia. 



b. The movements of the cilia in the isolated 

 cells or clumps of cells. Observe carefully the 

 cilia which are moving slowly; it may be 

 seen that the down-stroke (contraction) takes 

 place more quickly than the return (relaxa- 

 tion) ; there is no perceptible pause between 

 the two movements. 



c. The results of ciliary action. Granules and 

 blood-corpuscles are driven along ; detached 



L. 6 



