INTRODUCTION. 



ing the fluid with carmine or indigo, been able to detect in the 

 coloured particles surrounding the Diatom, those rotatory move- 

 ments which indicate, in the various species of true infusorial 

 animalcules, the presence of cilia. I am constrained to believe 

 that the movements of the Diatomaceae are owing to forces 

 operating within the frustule, and are probably connected with 

 the endosmotic and exosmotic action of the cell. The fluids 

 which are concerned in these actions must enter and be emitted 

 through the minute foramina at the extremities of the siliceous 

 valves ; and it may easily be conceived, that an exceedingly small 

 quantity of water expelled tlu-ough these minute apertures 

 would be sufficient to produce movements in bodies of so little 

 specific gravity. 



If the motion be produced by the exosmose taking place alter- 

 nately at one and the other extremity, while endosmose is pro- 

 ceeding at the other, an alternating movement would be the 

 result in frustides of a linear form ; while in others of an ellip- 

 tical or orbicular outline, in which foramina exist along the en- 

 tire line of sutiu-e, the movements, if any, must be UTCgular, 

 or slowly lateral. 



Such is precisely the case. The backward and forward move- 

 ments of the NaviculecB have been already described ; in Surirella 

 and Campylodiscus the motion never proceeds farther than a lan- 

 guid roll from one side to the other ; and in GompJwnema, in 

 which a foramen, fulfilling the nutritive office, is found at the 

 larger extremity only, the movement is a hardly perceptible 

 advance in intermitted jerks in the direction of the narrow end. 

 The subject is, however, one involved in much obscmity, and is 

 probably destined to remain, for some time to come, among the 

 mysteries of natm-e, which baffle while they excite inquuy. 



Section V. 



Self-division in the Diatomace^. 



This process, by which a single cell is converted into two per- 

 fect cells, is by no means peculiar to the Diatomacea?, but pre- 

 vails extensively in the vegetable kingdom, if indeed it be not 



