338 PROF. EHRENBERG ON ANIMALS OF THE CHALK 
servers, although the knowledge of the organic development of 
these forms is of essential importance for the establishment of the 
characters of the species, I think it will be useful to make more 
generally known, as early as possible, my late researches on their 
organization. The visible admission of indigo into the gastric 
cells of the Navicule by central exterior orifices, which I men- 
tioned in 1838 and had then observed in Closterie and Desmi- 
diacee and which I have succeeded in preserving as prepara- 
tions for general inspection, is indeed so decisive a proof of the 
animal nature of all these forms, that a sight of them is all that 
is requisite ; and the giving a bluish colour to some of their parts 
by tincture of iodine does not at all prove the vegetable nature 
of these bodies, since the possible reactions of this substance on 
organic matters are by no means fully known, even were micro- 
scopical observers always trustworthy chemists, and the colours 
produced determinable with sufficient accuracy, which frequently 
is not the case. Among the subordinate characters by which 
plants and animals are easily distinguished, may be considered 
not motion merely, but rather external organs of locomotion ; 
and the more so, when these may be exserted and retracted. 
At Cuxhaven there remained, in small pools left by the ebb 
of the tide, little bodies, which in form very much resembled 
Navicula (Surirella) elegans and striatula, but were essentially 
distinguished from the latter by their much larger size and 
the different sculpture of the shell. These animalcules, re- 
sembling a ribbed oval case of glass, and which belong to the 
largest species of Navicula, notwithstanding their size, ex- 
hibited great mobility, and I succeeded in discerning in them 
organs of motion far more distinctly than I had hitherto been 
able to do in other larger forms. These organs were likewise 
in shape and length very different from what I had hitherto ob- 
served in other Navicule. Instead of a snail-foot-like expanding 
sole, where the ribs or cross-bands of the shell join on to the rib- 
less lateral part of the shield, there were long projecting minute 
filaments, which the animal shortened or lengthened at will, or 
drew in entirely. An animal -{,th of a line in length, had on 
each side as many as twenty-four for each of the two plates, or, © 
in all, ninety-six such organs of locomotion; four also were 
visible on the broad frontal portion. The nutritive orifice ap- 
peared to be at the broad end. Whether other Surirelle possess 
similar organs of locomotion in definite number is not yet ascer-_ 
tained: nor have I been able to determine whether these organs 
