LOCOMOTION IN SURIRELLA. 



151 



But at length a ray of light came with a search for the 

 " Biitschli granules." This is not the place for a discussion 

 of the nature of these bodies. It must suffice that we recall 

 the fact that they are small granules moving about upon the 

 surface of protoplasm in livntig cells. Their motions are 

 apparently independent, and two of them may approach each 

 other upon the thinnest strand of quiescent protoplasm. Very 

 conspicuous bodies of this order occur plentifully in the 

 central sap-cavity of Siirirella, and other smaller granules, 



FiGURK II. (Adapted from I^auterbornl 



with similar motions, are to be seen sparingly on the outer 

 surface of the protoplasm, in contracted spaces between it 

 and the silicious membrane. Lauterborn states that he vainl}' 

 sought for such granules in the rib-canals, where indeed there 

 is quite enough space for them. I have been more fortunate. 

 In Figure II, one of these granules is indicated at G' and 

 another at G. Such a granule was first observed to run grad- 

 ually, and in a halting manner, nearly to the keel. It then 

 returned and disappeared toward the body of the valve. 



