le SOCIÉTÉ BELGE DE MICHOSCOIME. 



oily particles which fill-up the central space, while the 

 cndochrome remains in a perfectly fixcd position, through- 

 out the length of the frustules and bcneath the plasmie 

 mass. i hâve partially succeeded in demonstrating the 

 présence of a protoplasmic envelope by nsing various 

 magenta stains ; but I bave not obtained constant results. 

 On adding a drop of magenta stain to the spécimen 

 under the microscope, a délicate rose-pink colour is 

 qnickly communicated to the marginal portions of the 

 frustules, but neither the endochrome nor albuminoïd 

 globules are at ail affeçted by the stain du ring the life of 

 the Diatom. 



A number of brackish water Diatomace», Pleurosigma 

 ballicum, angulatum and quadratum, Swirella splen- 

 clicla, JSilzsckia, etc., readily took a simple stain of the 

 kind mentioned, and were thus rendered more attrac- 

 tive objects. The elongated wand-like bodies, which 

 serve to distinguish Bacillaria from most otbcr gênera, 

 take the stain, and the plasmie band which unités 

 its frustules together into a compact family is made 

 more évident. This genus exhibits a spécial modifica- 

 tion of another kind. The contractile Connecting fila- 

 ment is seen spread out into a broad band, which 

 completcly encloses the aggregate linear séries and at 

 the same lime becomes an intermediary layer of contrac- 

 tile tissue between each pair of frustules : at once an 

 example of cause and efî'ect, being the chief agent of pro- 

 gression and also of that remarkable sliding to and fro 

 motion, the counter part of the gliding movement per- 

 formed by Amœba. 



The greater buoyancy of some Diatoms, is possibly 

 owing to the larger quantity of oil globules contained in 



