170 VIGNETTES FROM INVISIBLE LIFE. 



vation to bear on their investigations; and have 

 thus elucidated many points of structure and 

 phases of life which might otherwise have been 

 overlooked. 



Thus, on the one hand, the peculiarities of the 

 Diatom's silicious valves, which seem to be perfo- 

 rated with minute foramina, or holes, have been 

 watched with almost feverish earnestness, in order to 

 discover whether or not any filmy processes ever pro- 

 trude, which might not only account for their move- 

 ments, but go a long way to prove their animal 

 nature ; and some observers have even asserted that 

 they have seen them. Even Julias Sachs, an eminent 

 authority, who classes them (the Diatoms) among 

 the vegetable tribes, thinks it probable that it is 

 by means of such protrusion of the internal soft 

 organic matter that their creeping and crawling 

 movements are effected. On the other hand, the 

 advocates of their vegetable nature find not only 

 that the special structure and functions which the 

 other side regard as peculiarly animal are also 

 found in undisputed vegetable organisms, but also 

 that they possess other undoubted vegetable charac- 

 teristics, which are but rarely found in conjunction 



