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ON THE MOVEMENTS OF THE DIATOM ACEiE. 
BY E. RAY LANKESTER. 
I T is but a few years since the power of movement was 
thought to be confined to and characteristic of animals 
alone, to the exclusion of both plants and minerals, and, indeed, 
the prevalence of this notion has left traces which are still very 
evident. Whilst the power of movement has been shown 
to be almost universally present among the lower cryptogamic 
plants, it is only in those cases where the presence of cilia 33 
has been observed and the organ of locomotion thus 
detected, that all doubt has been dispelled. In the case of 
the minute Desmidiaceas and Diatomacese, such mystery has 
veiled the cause of movement that the most ingenious 
and conflicting explanations of the phenomenon have been 
offered, the latter group of organisms being sometimes 
referred to the animal kingdom. In passing, it may be 
mentioned, that ee movement 33 is no longer to be considered 
as belonging even to animals and plants alone. The researches 
of Mr. Sorby have shown that in minute cavities contained in 
crystalline rocks rapid oscillations are continually going ou, 
owing to the movements of bubbles of air floating in liquid. 
The characters, however, of the movements exhibited by 
animals, plants, and minerals differ considerably, and there 
can be little doubt that careful observation only is needed to 
distinguish them. The movement in the mineral, whether of 
“ molecules,” as described by Robert Brown,* or such as 
noticed by Mr. Sorby, is dependent on the simplest external 
causes, either physical or chemical. In the plant, movement 
is either continuous and recurrent, or the result of momen- 
tary irritation, whilst in the lowest Rhizopod or Gregarina 
the movements exhibited are ever varying, and, apparently, 
are dependent on the most diverse causes. The object to be 
attained by the movement of both plants and animals may 
be broadly stated as either reproduction or nutrition, contact 
* Miscellaneous Botanical Works, Ray Society, 1866. 
VOL. V. NO. XXI. 2 E 
