88 GENERAL niSTORY OF THE INPUSORIA. 



perliaps should also be reckoned of the number, since he remarks, in his de- 

 scription of the shield of a Navlcula, that "such an artificial and complicated 

 structure amongst plants has no explanation, and is entirely without signifi- 

 cation. In all actual plants we find the silica present in quite a difi'erent 

 form, as little separate scales or drops, and distributed through the substance of 

 the cell-wall." 



In favour of the vegetable nature of the Diatomeae, on the other hand, the 

 majority of the original observers in this countrj^ unite mth many of the most 

 distinguished natui-alists of the Continent, such as Kiitzing, Siebold, Nageli, 

 Rabenhorst, Braun, Cohn, Meyen, &c. The last inquirer, so long ago as 1839, 

 urged various objections against the presumed animality of the Desmidieas 

 and Diatomeae, and more particularly against Ehrenberg's views. Respecting 

 the animality of the Diatomeae (Naviculacea), he remarks generally — " The 

 reasons adduced for such belief are so weak, that the conclusions deduced from 

 them are yet for the most part very doubtful." 



A small nimiber of natiu\alists have expressed the notion that the Diatomeae 

 belong equally to the animal and to the vegetable kingdom. M. Thuret may 

 be named as one of these, since he has stated that there is no more reason in 

 favour of the one afiinity than of the other. Such an idea is certainly unphilo- 

 sophical; for it would cut the knot instead of loosening it, by the assumption 

 of an order of organic beings intermediate between the animal and the vege- 

 table kingdom, and undeterminable to which they belong. 



We will now proceed to state the leading arguments for the animality of 

 the Diatomeae, indicating the name of the writer suggesting each, so far as 

 practicable : — 



1. The Diatomeae — many species at least — exhibit a peculiar spontaneous 

 movement; which is produced by certain locomotive organs. — Ehrenherg. 



2. The greater part have in the middle of the lateral surface an opening, 

 about which certain roimd corpuscles are situate, which become coloured blue 

 when placed in water containing indigo, like the ' stbmach-ceUs' of many In- 

 fusoria, and consequently may equally be regarded as stomachs. — Ehrenherg. 



3. The shells of many Diatomaceae resemble in structiu-e and conformation 

 the calcareous shells of Gasteropoda and similar Mollusca. — Ehrenherg. 



4. The method of multiplication by self- division. — EJirenhei^gandMeneghini. 



5. The complicated structure of the waU of the frustules, and the characters 

 of the silicious deposit. — Schleiden, Bailey, and Meneghini. 



6. The greater affinity in chemical composition of the contents (the endo- 

 chrome) with animal than with vegetable products. — Meneghini. 



Each of these arguments requires examination in detail, and its value tested. 

 To begin therefore with the first — the occuiTence of locomotion and the organs 

 by which it is effected, as e^ddences of animal constitution. Morren, in the 

 paper quoted {Jahreshericht Akad. Berlin, 1839), pointed out that motion is not 

 confined to animals, but exhibited also by the spores of Algae and by sperm- 

 atic particles. To these examples may be added the Oscillatoriae, Proto- 

 coccus in its various phases, Vaucheria clavata, Ulothrix zonata, and other 

 Algae, among which are the now admitted genera of Yolvocineae. In many 

 of these, the movements are much more active and lively, and present more 

 seeming spontaneity than those of any of the Diatoms. The employment of 

 the word spontaneous to signify the sort of movement of these organisms is 

 certainly unjustifiable, if understood at all in its usual signification, of an act 

 originating in the moving body directed to a special purpose ; for no more 

 spontaneity is manifested in the motions of these siKcious organisms than in 

 those of the leaves of the Dionc^a ^niiscijnda when any particle impinges on 

 their sensitive hairs. Meneghini, in examining this point, is compelled to 



