20 Myxophyceae 



within the original walls of the heterocyst. These are ultimately liberated, 

 and when set free they possess a very delicate membrane. 



Each gonidium may rest for a time or germinate at once to form a new 



filament. 



In the heterocystous Myocophycete of to-day that are living under normal 

 conditions of environment, the heterocysts appear to have no function other than 

 that of limiting the hormogones in certain types, and probably of limiting 

 the filaments themselves in the younger or adult stages of certain other types 1 . 



It is not improbable that heterocysts sometimes act as storehouses 

 for reserve materials of a protein nature, but there is no evidence to show 

 that this normally occurs under natural conditions. It is mostly in cultures 

 that such storage takes place. The position of the spores in the Rivulariacese 

 and in certain species of the genus Anabt&na, has led to the suggestion that 

 heterocysts are in some way connected with spore- formation, but this is 

 exceedingly doubtful. It has been suggested (Fritsch, '04 ; G. S. W., '04) 

 that heterocysts are probably the lingering and abortive relics of a type 

 of reproductive organ (gonidangium) once possessed by certain of the 

 Myxophyceae, but which long ago ceased to be functional. Brand's obser- 

 vations gave the first indication of this probable function ; Fritsch's evidence, 

 although slight, was not unimportant; and Spratt's observations on Anab&na 

 cycadearum are particularly important in this respect. A. cycadearum is 

 a profoundly modified species of Anabama, living under such extraordinary 

 conditions that the filaments have greatly degenerated and the heterocysts 

 have apparently reverted back to their original function of gonidangia. 

 Attention should also be directed to the position of the heterocysts in 

 Nostochopsis (fig. 11, A and B). They are lateral, and either stalked or sessile, 

 being strangely reminiscent of the position of gonidangia in many of the 

 Green Alg*. 



SPONTANEOUS MOVEMENTS IN THE OSCILLATORIACE.E. Certain Blue- 

 green Algse of the family Oscillatoriacese exhibit spontaneous movements, 

 generally of a slow oscillating, gliding, or rotatory character. It is in the 

 genus Oscillatoria that these movements are most easily observed, but 

 although they have been repeatedly investigated, no convincing explanation 

 has yet been offered. The movements exhibited by some species of 

 Oscillatoria are of three kinds : a gliding or creeping movement by which 

 the whole filament travels slowly through the water in a serpentine manner, 

 either forwards or backwards; a slow oscillation of a considerable portion 

 of the apical part of the filament ; and a rather more rapid bending of the 

 extreme apex which generally closes each oscillation. 



1 Young Nostocs are always limited by heterocysts. 



