Cytology and Movements of the Cyanophycee. 311 
by alternate shortening and stretching of the opposite halves 
of the cells. and depending partly on the living energy of the 
cells and partly on the ductility and elasticity of their mem- 
branes.” In another place (17) he carried out the same 
idea of expansion and contraction as follows: “Flexible 
Oscillaria filaments are capable of bending themselves spon- 
taneously and of stretching themselves either straight out 
or curving themselves into snake-like forms, or entwining 
around other filaments.” He could faintly make out a 
delicate protoplasmic pellicle covering the whole trichome. 
The unequal contraction of this pellicle assisted to cause 
the unequal contractions noted. 
Hansgirg (35) concluded that motion was due to heat 
and light. The creeping movements took place within a 
very thin gelatinous sheath which fastened itself to some 
substratum and the organism moved backwards and for- 
wards in this, leaving it extended behind the organism in a 
reed-like tube. This substantiated the observations of 
Schultze (70), though he considered the reed-like tube to 
be visible only on the sharpest inspection. This surrounding 
layer of slime was considered to be the same as that which 
Engelmann (22) described as a surrounding protoplasmic 
layer, though on account of its different stainability with 
iodine, Hansgirg concluded that it was not protoplasmic. 
Further, if the organism was cultivated in darkness, this 
sheath of slime disappeared and the organism lost its 
motility. He thought the force, which caused the various 
movements of Osctllaria, was generated by osmotic currents 
passing into the protoplasm of the filament. ‘For,’ he 
continued, “I have established by definite observations that 
a powerful strength of imbibition is peculiar to the pro- 
toplasmic content of the cells of this organism, and this 
strength of imbibition works as long as the cell lives.” 
And again he said: “According to my view, the move- 
ments of those Oscillaria filaments which are enclosed 
in an osmotic sheath in which they move backward and 
