Mucus-substance of the Cell in the Characese. 121 



owing to an innate contractility, and not to any foreign organism 

 or any other moving power, is much more satisfactory than if 

 it were unsupported by the movement of the mucus-layer in 

 SpirogyrOj w^here its nature is obvious from the object gained 

 by it. 



I allude to the movements which take place in Spirogyra 

 during conjugation, when the mucus-layer, retracting from the 

 cell-wall of one filament, carries its contents through the tube of 

 intercommunication, across to the cell of the opposite filament. 



To refresh the memory of the reader, 1 might here briefly sum 

 up what takes place on this occasion. The first step on the 

 part of the mucus or protoplasmic layer is to soften a small por- 

 tion of the cell-wall ; it then presses upon this so as to force it 

 forwards into a tubular prolongation to meet a similar one from 

 the opposite filament ; the two mucus-layers dissolve the par- 

 tition which interrupts their union ; the mucus-layer of one cell 

 then retracts from its cell-wall, gathers up the spiral bands and 

 cytoblast, and mingling with its fellow at the junction of the 

 tubular prolongations, passes over into the opposite cell with the 

 return of the latter, and there amalgamating with it thoroughly, 

 becomes capsuled and passes into a spherical or elliptical spore, 

 as the case may be. Now here there is no addition of material 

 to cause the mucus-layer to grow and protrude from its cell like 

 a bud or young shoot, — it is an act performed by the mucus-layer 

 alone, and that too almost faster than the hour-hand travels 

 round the dial of a watch ; indeed, it is performed so quickly in 

 Closterium Ehrenbergii, where a similar process takes place, that 

 according to the Rev. W. Smith, who has watched it, the dis- 

 charge of the endochrome and formation of the sporangia are 

 accomplished with such rapidity, that this may be seen to take 

 place in the field of the microscope, " the whole operation not 

 occupying more than a few minutes*." 



Again, in CEdogonium flavescens (Kg.), I was lately fortunate 

 enough to see the contents of one of the cells wrapped up in 

 their protoplasmic sac, actually leave the cell, form into a spore, 

 and whirl off in the manner of zoospores generally. The cell- 

 wall bore no appearance of spore-dilatation, though the density 

 of the gonimic contents indicated that it would sooner or later 

 have done so ; it was a terminal one, and the septum of the free 

 end had probably been broken when the other part of the fila- 

 ment had been torn from it in preparing the mass for microsco- 

 pical examination. As the last part of the cell-contents left their 

 old cavity distinct locomotion was seen in the mass, and when 

 the whole had become extricated, several twitchings of the pro- 



* Ann. and Mag. Nat. Hist. vol. v. p. 8, 1850. 



