176 ROMANCE OF LOW LIFE AMONGST PLANTS. 



been abandoned, no entirely satisfactory explanation 

 of the causes of motion has been promulgated. The 

 general view is that the movements are owing to 

 forces operating within the frustule, and probably 

 connected with the endosmotic and exosmotic action 

 of the cell. Professor Smith was of this opinion, 

 and his work still ranks as a text-book of British 

 Diatomaceae ; and he believed that the fluids con- 

 cerned in these actions must enter and be emitted 

 through the minute foramina at the extremities of the 

 siliceous valves. It may easily be conceived that an 

 exceedingly small quantity of water expelled through 

 these minute apertures would be sufficient to produce 

 movements in bodies of so little specific gravity. 



The following is a summary of the arguments 

 which have been adduced in favour of the animal 

 nature of diatoms : — 



1. The Diatomaceae — many species at least — ex- 

 hibit a peculiar spontaneous movement, which is 

 produced by certain locomotive organs. 



2. The greater part have in the middle of the 

 lateral surface an opening about which certain round 

 corpuscles are situate, which become coloured blue 

 when placed in water containing indigo, like the 

 stomach-cells of many Infusoria, and consequently 

 may equally be regarded as stomachs. 



3. The shells of many Diatomaceae resemble in 

 structure and conformation the calcareous shells of 

 Gasteropoda and similar Molluscs. 



4. The method of multiplication by self- division. 



5. The complicated structure of the wall of the 

 frustules, and the characters of the siliceous deposit. 



