OF THE DIATOME^. 57 



seem, as an excretion from the organic membrane of the frustiiles, indicates 

 the activity and energy of the nutritive fimctions, — a fact further demonstrated 

 by the production of the ' connecting membrane/ and, in short, by the whole 

 process of reproduction, whether by self-di^dsion or by sporangia. The silica 

 present in the lorica must be taken up by the organism in a state of solu- 

 tion ; and although the quantity of silica dissolved in water is inconceivably 

 small, it is nevertheless sufficient to supply the material for the construction 

 of millions of Diatomaceous shells, even in a short time, as the phenomena 

 of reproduction and the rapid appearance of these structures as an appre- 

 ciable powder, or as a coloui'ing matter in water, prove. " It is probable," says 

 Dr. Gregory {J. M. S. 1855, p. 2), " that as fast as the silex is extracted from 

 the water hj them, it is dissolved from the rocks or earths in contact mth 

 the water, so that the supply never fails ;" and we may add, so that the 

 quantity never accimiulates beyond the very minute fi^actional portion chemists 

 can detect. 



Ehrenberg's untenable hypothesis of the presence of stomach-sacs and of an 

 alimentary canal opening externally has received sufficient attention in the 

 history ah^eady given (pp. 47, 48), of the natiu^e of the contents of the Diatomeae 

 and of their investing lorica. "Were other considerations needed, the absence 

 at times of any such vesicles as Ehrenberg conceived to be gastric cells, their 

 occasional coalescence, and the phenomenon of cyclosis or the circulation of 

 the contents, each and all subjects of direct obsei^ation, might be appealed 

 to as proofs of the errors that great naturalist fell into respecting the internal 

 organization of the Diatomeae. 



The phenomenon of cyclosis has been observed by Niigeli in a species of 

 Navicida, and in one of GallioneUa {Melosira) (XY. 27), and by Prof. Smith 

 in other Diatoms. This writer says {op. cit. i. p. xxi) — " In SurireUa biseriata 

 this motion has been more especially apparent ; but I have also observed it 

 take place in Nitzsclda scalaris and Camj)i/lodiscus scalaris. This cii^culation 

 has not, however, the regularity of movement so conspicuous in the Des- 

 midieee, and is of too ambiguous a character to fuiTiish data for any veiy certain 

 conclusions, save one, viz. that the Diatom must be a single cell, and cannot 

 contain a number of separate organs, such as have been alleged to occupy its 

 interior, — since the endochrome moves fi^eely from one portion of the frustule 

 to the other, approaching and receding from the central nucleus unimpeded 

 by any intervening obstacle." 



Schultze, in his contribution on the movements within the frustules of 

 Diatomeae {Midi. Arcliiv, 1858), represents them to occur in and along the 

 finely granular threads into which the less fluid mucilaginous portion of the 

 endochrome is di^awn out. He compares the movements in character to 

 those of the ' variable processes ' or pseudopoda of Ehizopodes, and thereby 

 assimilates the mucilaginous films of Diatomaceous fnistules with the soft 

 sarcode of those simplest animalcules, — a similarity countenanced by the now 

 weU-known fact of an Amoebiform phase in the cycle of development of some 

 of the lower Algae {vide section on Phytozoa). The cyclosis in plant-ceUs is 

 no doubt rightly attributed to the operation of the vital processes of nutrition 

 and of the so-called respiration, and primarily to the chemico-vital action 

 proceeding by the medium of the chlorophyU-globules ; and it seems most con- 

 sonant with the teachings of science to assign the less active and less complete 

 and regular internal movements of the Diatomeae also to the similar vital 

 forces, — the coloured corpuscles, it may be, acting here likewise as the prime 

 mover. We are aware that the nucleus has been represented to be the first 

 source of the movements in plant- cells, since the current seems to flow from 

 and to return to it in many cases ; but this phenomenon is explicable in 



