156 PALMER: 



the glass may play its part, this diatom can also retain its 

 hold when one end sinks down somewhat, so that the longer 

 axis makes an acute angle with the glass. In India ink 

 emulsion, minute particles of the ink follow down the raphe 

 to the contact nodule, at which point they collect in the slight 

 depression and are finally squeezed out to the side of the 

 valve in the form of a small, irregular mass, evidently 

 cemented with slime. At the same time (and this is most 

 unexpected) a similar stream, but not so pronounced, runs 

 from the after end of the valve to the central nodule, ifi the 

 directioyi of the motion of the diatom, and the ink particles so 

 arriving help to form the little masses already described. 

 This stream would appear, on careful focussing, not to be in 

 quite such close contact with the glass as that coming from 

 the front end. At times the diatom conies almost to rest, 

 there is evidence of a struggle, and with a sudden jerk the 

 crawling proceeds. We have here to do with a sticking fast 

 to the glass and a rupture of the slime which is giving the 

 trouble. This diatom crawls rapidly and surely, and is able 

 to push loose other species not so securely applied to the glass 

 by broad surfaces. Yet if by any means it entirely loses con- 

 trol it sinks through the water at once, and falls upon the 

 bottom of the cell. It is too small a form to promise much 

 light on the problem of motile mechanism. But so far as one 

 is able to see, the phenomena described are quite well recon- 

 cilable with the general view that a stream of protoplasm 

 along the raphe is the actuating element. 



Navicula socialis. Although this diatom is described as 

 occurring in flat, tabular groups of four frustules, frecpiently 

 groups are seen in end view to be slightly curved. Some- 

 times, also, one frustule of a group will be bent out of the 

 plane of the other three, even to the extent of 90°. A less 

 pronounced example of this last condition is represented at i 

 in the diagram, the view being a median cross-section of the 

 group. These aggregations are surrounded by a common 

 nimbus of coleoderm, and the contact with the cover glass is 



