58 GENEEAL HISTORY OP THE INFUSOllIA. 



another way, by admitting the disposition of the mucous threads as displayed 

 by Schultze, extending as they do from the nucleus on all sides, and serving 

 at the same time to limit and to direct the movements taking place within 

 and by them. We have not adverted to ciliary action as the cause, for ; so 

 far as we can gather, Mr. Osborne and Mr. Jabez Hogg have failed to impress 

 many naturalists with the fact of its existence and operation in Diatoms. 



Lastly, Schultze remarks that, to see the mucilaginous threads and the 

 internal movements, living and fi^esh specimens are needed ; for they are soon 

 arrested when the frustules are removed from their natui-al habitats, and are 

 quite lost to vision when they become diy. Hence it is, no doubt, that no 

 previous observer has detected and rightly apprehended the facts enunciated 

 by Schultze. 



The so-called function of respiration is evinced in the fixing of the carbon 

 of the carbonic acid and in the disengagement of oxygen gas ; but this is 

 rather an act of nutrition, and resembles that silent and invisible disengage- 

 ment of certain particles, and the rearrangement of others, which proceed in 

 the formation and in the removal of worn-out tissues in higher animals. 



MuLTiPLiCATiois", REPRonrcTio:?^, AifD Developmej^t of DiATOMEiE. — Among 

 the modes of reproduction of the Diatomeee, self- division has usually been 

 accoimted one, but erroneously so, since this process is no more than a mul- 

 tiplication of an individual cell, and completely homologous with the process 

 of cell-fission exhibited in the construction of animal and vegetable tissues 

 in general. The peculiarity in the self-division of the Diatomeae, i e. among 

 the free simple beings, is, that the division is followed by separation ; for 

 each cell, instead of imiting Avith its neighbours in the formation of a tissue, 

 commences an independent existence. Self-division in one direction, not 

 followed by separation, produces the filamentary or concatenated Diatomeae, 

 whilst the abundant excretion of a mucus around the dividing frustules, and 

 its persistence, give rise to the frondose genera, which make an approach 

 towards the character of vegetable cellular tissue, — each ceU, however, retain- 

 ing an independent vitality greatly more pronounced than in the latter. 



The process of self-fission or deduplication in this family resembles in all 

 essential particulars that in other vegetable cells (XY. 28, a, h, c). Preparatory 

 to its visible occurrence, or rather simultaneously Tvith certain changes in the 

 interior, the valves separate by the progressive gro^i;h of the connecting 

 membrane. The nucleus within is observed to divide into two portions, each 

 of which eventually becomes detached from the other, and, in Prof. Owen's 

 language, serves as a centre of spermatic force, and induces an aggregation 

 of the granules of the endochrome about it. Whilst this separation of the 

 nucleus and of the general contents is going forward, the lining or primordial 

 membrane of the cell becomes doubled inwards in the entire cii'cumference 

 along the line of division, and advances gradually until it at length forms a 

 complete septum, cutting the original single cell into two. This septum is 

 actually double ; and in each lamina a deposit of silicious material speedily 

 proceeds, so as to produce two new valves, each opposed to, and immediately 

 continuous around its circumference with, one of the two original valves. 

 Thus, on the completion of this process of deduplication, two finistules result, 

 awaiting only the final act of separation to enter on an independent exist- 

 ence and to repeat the like series of phenomena, and so on through a 

 seemingly almost endless chain, to perj)etuate the existence of the particular 

 species or individual. (See Meneghini's account of the process and peculiari- 

 ties of self-di\dsion in this class, in the examination of the argimients for the 

 animality of the Diatomaceae, in a subsequent page.) The true nature, there- 

 fore, of this process of self-di\-ision being an extension, not a renewal, of 



