262 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Movements of Oscillariese.* — A. Hansgirg has investigated the 

 cause of the movements of OscillarieaB, and especially their relationship 

 to light. The filaments of 0. Frolichii, placed in complete darkness, 

 were found to have lost on the second day their mucilaginous envelope, 

 and to have sunk to the bottom of the vessel. The twisting and 

 creeping movements, however, continued till the seventh or eighth 

 day, becoming gradually weaker. The more sensitive filaments of 

 0. cerugineo-ccerulea lost their power of motion more rapidly. In 

 direct sunshine the movements were more lively than in diffused day- 

 light. An increase in temperature of the water also promoted the 

 rapidity of the movement. 



The separate filaments of a cluster move with different degrees of 

 rapidity, depending not only on warmth and light, but also on the age 

 of the filament ; the quality of the water, whether spring, river, or 

 stagnant water, also has an effect. The twisting and nodding move- 

 ments the author believes to be due, not to their growth, but to 

 osmotic changes in the cell-contents. The creeping movements, he 

 holds, cannot be due to protrusions of the internal protoplasm, since 

 each filament is enveloped in a gelatinous sheath, which is not com- 

 posed of protoplasm. The cells also exhibit motion when the envelope 

 itself is at rest. The movements must originate in the protoplasmic 

 contents themselves of the cell, and are probably of the same nature 

 as those of the sarcode in the so-called pseudopodia of rhizopods and 

 other protozoa. 



Movements of Diatoms. t — Dr. J. Hogg comes to the conclusion 

 that these movements are not to be explained upon any endosmotic 

 and exosmotic theory or on that of an undulating protoplasmic 

 membrane ; nor are they due to cilia arranged throughout the 

 sutural line of the frustule or projecting from the openings at the 

 extremities. In his view the movements are caused by contractile 

 prehensile filaments. 



" By attentively following a diatom, under high power magnifi- 

 cation and careful illumination, its movements are seen to be under 

 its own control. It will attack a body relatively larger than itself ; 

 it will force the sharp or taper end of its frustule into a mass of 

 matter, and recede from it, with a jerky motion. This action it will 

 repeat many times over or until it has opened a way for itself. Such 

 movements will be explained by the alternate extension and retraction 

 of a delicately constructed prehensile organ, or organs, contractile 

 prehensile filaments, protruding through an opening or operating on 

 the external surface of the siliceous frustule. It is but necessary to 

 have prehensile filaments capable of extension, in the transverse 

 direction of each half of the frustule, to which they may be attached, 

 to further comprehend the forward and backward movements per- 

 formed by the diatom. For a nearly parallel example I may refer 

 to the pediculate rotifer : the pedicle of which consists of a highly 

 contractile spiral style. This the rotifer alternately expands and 



* SB. K. Bohm. Ges. Wiss. Prag, June 9, 1882. See Bot. Oentralbl., xii. 

 (1882) p. 861. 



t Sep. repr. from Mem. Soc. Belg. de Micr., 1883, 11 pp. Cf. Keport of 

 Referee in Bull. Soc. Bdg. Micr., ix. (188R) pp. 37-44. 



