Mucus-substance of the Cell in the Characese. 119 



proofs of the mucus-layer,, minus the rhizopodous cells, pos- 

 sessing the " inherent power of mobility '' mentioned at p. 18, 

 which was then assigned to it, chiefly upon the inference that 

 the mucus of the mucus- layer furnished the cell- wall of the so- 

 called " gonidial cells/' and that the polymorphic and locomotive 

 power of the latter at the commencement was indicative of the 

 same power existing in the mucus in its amorphous, plasmic 

 state. That such a deduction would be inadmissible if the 

 development was to be considered infusorial, I stated in my 

 '^ Postscript '' (p. 22) ; and now that the so-called " gonidial 

 cells '' have been shown to be the globular vesicles of the mucus- 

 layer, and of a rhizopodous nature, the fallacy of such an infer- 

 ence is much more evident. But I also observed, that there 

 were still " sufficient reasons left '' for my considering the rota- 

 tory motion of the mucus-layer due to an independent con- 

 tractility. 



I have now to give further proof of this ; but, unfortunately, 

 in doing so I must confine myself to what the mucus-layer 

 exhibits while within the internodes and roots of the young 

 plant, supported by what it may be inferred to possess from 

 analogous motions exhibited by the mucus-layer of other allied 

 organisms ; for the cells and the roots of the young plant, at 

 that time when alone we have the power of determining that 

 there are no rhizopodous cells in them, furnish too small a 

 quantity of mucus for our watching it in the manner so easily 

 effected when issuing from the large internode. 



To pursue this inquiry, then, we have first to satisfy our- 

 selves that the motions in Nitella and its allied organisms are 

 in homologous structures, and then to see how many kinds of 

 motion this structure presents. 



Of their being in homologous structures there can be no 

 doubt, because the mucus-layer in all is the protoplasm of the 

 cell ; and they are of two kinds, viz. one of general irritability, 

 and the other of polymorphic and locomotive power. 



The first kind, or that of general irritability, is manifested by 

 the trembling movement of the granules which are imbedded in 

 the mucus-layer itself, more than by that of the moving agent 

 or mucus, which can hardly be seen, from its transparency. 

 This motion of the granules, which is similar to that termed 

 " molecular,^' is observed in the mucus-layer of the spine-cells 

 of Nitella in which no circulation has ever existed, and in that of 

 the internodes when the circulation is temporarily arrested. It 

 is also seen in Cladophora, and particularly in Spirogyra ; in the 

 Desmidise [Closterium, &c.) ; in the Diatomacese {Navicuhj &c.), 

 and in the mucus of the cell of Spongilla, &c. 



The second kind, or that of polymorphism and locomotion. 



