114 PROCEEDINGS OF THE ACADEMY OF [1898. 



The forward movement of Eunotia resembles very little the 

 smooth gliding of Pinnularia and Nitzschia. If these seem to swim, 

 the other would appear to crawl. One corner is advanced a trifle, 

 then the other corner, then both move forward at once. Occasion- 

 ally the frustule will sidle for a moment ; but generally the pro- 

 gression consists of a succession of impulsive jerks. The movement 

 is accompanied by indications of very considerable stress. Compar- 

 atively large bodies, such as short filaments of Eunotia or small 

 particles of sand, are pushed resolutely aside. Larger bodies, espe- 

 cially such as have considerable thickness, arrest the frustule for a 

 time ; but after a short interval, it is apt to turn upon its edge, with 

 ventral girdle in contact with the obstruction, to move past in this 

 position, and once more to resume its normal relations with the 

 slide. At the moment of the passage of the anterior, and sometimes 

 the posterior end of the frustule, the obstruction may be seen to 

 move backward, as if from an impulse resembling a kick. These 

 curious features I have observed numberless times. 



If by chance the moving cell pass, as in fig. 1, PI. VI, with a 

 corner over the circumference of a thin piece of mica, the latter is, 

 in many cases, caused to revolve backward in the direction indicated 

 in the figure. This also was seen so often that the existence of some- 

 thing resembling pseudopodia at the corners of the frustule came to 

 be anticipated with confidence. 



Many species of motile diatoms, among them Pinnularia and Nit- 

 zschia, exhibit a sort of pendulum movement. The frustule proceeds 

 in a straight line a certain time, comes to rest, and returns upon its 

 path without changing the direction of its longer axis. This swing 

 to and fro is repeated any number of times, so that anterior and pos- 

 terior ends continually change places. There is little of this in the 

 movement of Eunotia. I have frequently followed a frustule for 

 half an hour without seeing it return upon its path, and on one oc- 

 casion I observed a particularly active individual for two and a half 

 hours, in which period its devious way was into all portions of the 

 hollowed slide, and in all that time it kept one and the same end 

 foremost. Yet there seems to be no universal necessity for this 

 habit, since frustules are frequently observed to exhibit propulsive 

 efforts upon solid bodies from both ends, and occasionally they do 

 reverse their direction. 



Movements in the hanging drop. — In order to study somewhat 

 further the relations between moving Eunotia and the glass of the 



