1894.] MICROSCOPICAL JOURNAL. 239 



tissues supporting or carrying tlie granules have a re- 

 tractile and contractile power. Frequently, while being 

 observed, the sigmoid line of granules may be expanded 

 as if by a twitch-like movement to twice its former dis- 

 tance from the shell, since the sides of the siliceous 

 frustule are strictly parallel. The estimation of the 

 amount of expansive deflection of the sigmoid line of 

 granules is very marked, and the deflection of the lines 

 where they dip into and emerge from the nodular cavity 

 is also very marked when the flow is active. Under 

 favorable conditions the phenomenon of the pseudo- 

 ciliary action is beautifully shown along the pleural 

 fringes or zones. From the outer or second zone of 

 exoplasmic activity, the full width of the fringe con- 

 taining the active carbon granules may be seen to be 

 rapidly cleared up by a spinning flow. This diverts all 

 of the India ink granules to the extremity of a short arc- 

 like thread that pours its current of granules into the 

 nodular depression, and outwards again towards the 

 passive end of the frustule. If the attention is now 

 drawn to the anterior moving (active) prow, the pseudo- 

 podial flow of the exoplasm (ectoderm) may be observed 

 as long as desirable. This is closely analogous to that of 

 an active moving amoeba proteus or naked amoeba. When 

 merely moving without feeding, the ectoderm will seem 

 to be bunched up like the advancing waves before the 

 bow of a river steamboat and insinuating itself irregu- 

 larly as well as expansively among the granules of car- 

 bon. This rapidly causes them to stream away to the 

 right or left, and usually evenly parts them at the mid- 

 dle of its axial line of travel. The carbon granules do 

 not infringe against the siliceous frustule unless drawn 

 in there at the will of the diatom. The efi'ect of the 

 flowing, advancing exoplasmic mass is to act on the 

 granules as if blown away, rather than as if driven ofi'by 

 ciliary action. The latter is readily noticed among the 



