ADDENDA. 



In addition to note on page 16 the following may be quoted 

 from the "Journal of the Eoyal Microscopical Society of Lon- 

 don," Feb., 1884. It relates to the motion of granules in the 

 vacuoles of Glosterium. 



The occurrence of crystals of calcium sulphate, endowed with 

 a peculiar dancing motion, has long been known in the terminal 

 vesicles of Glosterium and in other desmids ; the phenomenon has 

 now been carefully investigated by A. Fisher. Their chemical 

 constitution was clearly established by different tests. They 

 are always quite isolated from one another, and occur in all 

 parts of the cells, though in the greatest quantity in the terminal 

 vesicles ; they are either carried along passively by the currents 

 of protoplasm, or they swarm in the space filled with cell -sap, be- 

 tween the cell wall and the radiating chlorophyl bodies ; these 

 vesicles are not true vacuoles, but portions of cell-sap space. 

 The crytals are not formed, nor do they grow, in the vesicle, 

 but reach it in a mature condition from some other part of the 

 cell, being formed apparently in the furrows between the bands 

 of the chlorophyl bodies ; from here they are carried to the ter- 

 minal chambers of the protoplasmic currents. 



Fisher found these crystals in all species of Glosterium which 

 he examined, also in various species of Gosmarium (though indi- 

 viduals are often entirely destitute of them) their form being 

 the same as in Glosterium. They occur in Micrasterias, Euas- 

 trum, in which genera also they are not invariably present, and 

 always in Pleurotaenium, Fenium and Tetmenwrus, but were absent 

 from all the specimens examined of Staurastrum, Desmidium and 

 Hyalotheca. They appear to be entirely confined to the Des- 

 midieae, other fresh water Algae containing calcium oxalate, 

 especially species of Spirogyra, but not calcium sulphate. 



Desmidium diagonum (Aptogonum diagonum). 



Filaments compressed, perforated, twisted, not vaginate ; 

 cells in end view oblong elliptic. 



Diameter 32 pi. ; thickness 14 yu. ; length of cell about half 

 the diameter. 



171 



