496 EXPLANATION OF THE PLATES. 



membrane, and are bounded externally by the mucila- 

 ginous layer ; d y living, unaltered contents, lying upon 

 the walls ; e, mucilaginous cord, the remains of the 

 mucilaginous layer formerly clothing the points a ; it con- 

 nects c and d. 



2. The same piece of tube as in Fig. 1, a short time 

 after. The mucilaginous cord (1, e) is torn in two, and 

 has become united with the two living portions of con- 

 tents (c and d). 



3. Piece of an old tube, in which the whole contents 

 have become detached from the membrane ; the greater 

 part is dead and beginning to dissolve ; a, a, little, colour- 

 less, globular masses of mucilage ; b, b, the same larger, 

 granular, and of a pale green, with a delicate membrane ; 

 c, c, distinct cells, with green granular contents deposited 

 upon the walls. 



Figs. 4, 6. Zygnema stettinum Ag. 



4. Piece of a filament, where the conjugation has not 

 been perfectly effected. The contents have become ag- 

 glomerated into a ball, and converted into a cell in each 

 articulation, these cells exhibiting the same form as the 

 contents accidentally possessed before the formation of the 

 membrane. In a it is ellipsoidal, in b and c, furnished 

 with a papilla corresponding to the blind process. 



6. Two articulations of distinct filaments which have 

 conjugated. The contents of both articulations had 

 been transformed into cells before the union. The con- 

 tents of the articulation a have become an ellipsoidal cell. 

 The contents of b have produced a cell in the same form 

 which they possessed during their passage through the 

 tube of communication. 



Kg. 5. Spirogym quinina Link. 



Piece of a filament in which the germ-cells form with- 

 out congregation. The contents have been loosened from 



