OF THE DIATOME.E. oYf 



admit that no absolute proof is deducible from the movements of the fmstules, 

 in support of their animal nature ; and the only difficulty to him against 

 admitting that they may be vegetable in character, is, that they are so dif- 

 ferent from those of Oscillatoriae, Desmidiese, and Protocoecoidese, — a worth- 

 less objection, to be sufficiently answered by asking whether that motion does 

 not diifer as widely from that of any -animals, and whether the movements of 

 the Desmidieee are not equally unlike those of the OscillatoriaB as those of the 

 Protococciis. 



The locomotive organs insisted on — consisting, according to Ehrenberg, of a 

 retractile foot and of retractile ciliary processes — have not been sufficiently 

 demonstrated to use as an argument. Ehrenberg, Corda, and more lately 

 Focke, are the only observers who pretend to have seen such organs, although 

 the organisms said to possess them are subjects of daily minute research by 

 hundreds of wonder-finding microscopists. The mucous film which invests 

 many Diatomaceous fmstules may, indeed, have been seen and misinterpreted. 

 Meneghini calls attention to a kind of sparkling or agitation — actually a rapid 

 and indeterminate change in the refraction of light at their extremities, which 

 he seems disposed to believe shadows forth the presence there of some sort 

 of ciliaiy locomotive organs. Granting, however, that cilia were ascertained to 

 be the cause of the movements perceived, the doctrine of animality would in 

 no way be advantaged, since cilia are not peculiarly animal structures. 



According to Nageli, one sort of vegetable movements originates in the act 

 of growth. Of such a kind are probably the \ibrations of the Oscillatoriae ; and 

 possibly the motions of the Diatoms are in some degree reducible to the same 

 category. And it is to be remarked that these motions are not equally apparent 

 and active under all circumstances, even among specimens of the same species, 

 but are most so when the vital phenomena of the organisms are most aroused — 

 when the most rapid interchange of material is going on between the external 

 medium and the internal cavity. 



2. The second argument rests entirely upon hj^^othetical grounds, derived 

 from Ehrenberg's observations, and is valueless so long as those observations 

 are imconfirmed. It seems quite clear that the central opening or umbilicus 

 spoken of has no real existence ; and if this be so, then the apparent entrance 

 of coloming matter within a set of corpuscles situated around it must be an 

 error of obsei-vation, unless the unproved and improbable assumption be made 

 that the coloui'-particles enter at foramina placed elsewhere (as at the extre- 

 mities), and become transmitted to these centrally placed sacs or so-called 

 stomachs. Kiitzing declares that the seeming entrance of colour-granules is 

 the result of mechanical causes, and adds the more important statement that 

 the central collection of vesicles is often wanting. 



3. The third argument, that a resemblance obtains between the shells of 

 Bacillaria and those of some Molluscous animals, is, to say the least, fanciful, 

 and in a scientific inquiry can be admitted to prove nothing. If external 

 similarity proved anything, it might as weU be adduced to demonstrate the 

 affinity of a lead-tree with the higher plants, whilst, again, the error to which 

 this sort of proof wiU lead is well exemplified in the case of the Eoraminifera, 

 which from mere outward resemblance were for years accounted members of 

 the Cephalopodous family. In the latter instance, indeed, the similarity in 

 external form was very striking — far exceeding that of any Diatom with any 

 testaceous animal. 



Kiitzing, in his review of this assigned reason for their animality, meets it 

 in another way, by observing that, among the cells of higher plants, examples 

 are to be found which in configui^ation and other particulars agree mth Dia- 

 toms — for instance, the numerous forms of pollen with their angles, spines. 



