384 PEOF. TH. W. ENGELMANN. 



there are often larger lumps of substance like spindle-shaped 

 swellings, or lateral prominences of a thread moving in the 

 same way as the granules. Foreign bodies, which have got 

 stuck to the thread substance and taken in, partake also of the 

 movement. 



'' Thc' greatest rapidity of single granules hitherto observed 

 (Schultze in Miliola) attains 0-03 mm. in a second. Generally 

 it is considerably less. It is extremely sluggish for instance in 

 sun animalcules." 



Gliding movement.^ — The peculiarity of this case is that 

 on the outside of a firm cell integument, extremely thin layers 

 of protoplasm devoid of granules move along, and by means of 

 their movement the whole body progresses upon a firm basis in 

 a gliding or creeping manner; relatively solid bodies which 

 remain sticking to this layer can be moved onwards along its 

 upper surface. The direction of the movement is generally 

 straight forward (Diatoms) or spiral (Oscillatoria), sometimes 

 backwards sometimes forwards. The rapidity seldom exceeds 

 0'04 mm. in a second. It is almost continually changing in 

 the same individual. The force with which the movement 

 takes place may attain a considerable amount. This type of 

 movement is exhibited by most Bacillaria (rocking movement 

 of Diatoms) and Oscillatoria as well as by young stages of 

 Nostocacese and Rivularise. 



The superficial protoplasm of these organisms is during life 

 it appears, never visible, on account of its extreme thin- 

 ness and low refractive power. Its presence was formerly 

 inferred only, on account of the movement produced.^ In 

 many cases it is only rendered visible by means which produce 

 coagulation.^ 



1 Many botanists, following Nageli's example, use this term to express the 

 streaming of granules on the surface of threads of protoplasm. 



2 Max Schultze, " Ueber die Bewegungeu d. Diatomeen," ' Arch. f. Mikr. 

 Anat.,' i, pp. 376—402, pi. xxiii, 1865. 



^ Th, W. Engelmann, * Ueber die Bewegungen der Oscillarien und Dia- 

 tomeen," ' Arch. f. d; ges. Physiol.,' xix, p. 8, 1878. 



