Dixon & Joty—On Some Minute Organisms. 745 
foregoing figures will explain the form of the coccolith. It will 
be noticed that the connecting stalk between the two valves is much 
shorter than that given in the figures of Biitschli, and that it is 
scarcely correct to describe these bodies as*resembling a shirt-stud 
in shape.’ 
The coccoliths dissolve quickly in dilute hydrochloric acid, and 
are partially and much more slowly attacked by strong caustic 
potash. The latter reagent does not appear to be able to com- 
pletely dissolve the central parts, more especially of the small 
valve, or, at least, cannot do so with any celerity. The absence 
of the appearance of free gas upon attack with acids hardly 
negatives the generally accepted view that these bodies are calca- 
reous. In all these tests we have frequently had characteristic 
Diatoms present in the same field ; and whereas the siliceous valves 
of the Jatter were unaltered by the acid, the coccoliths were quickly 
dissolved. In the application of the caustic potash test, diatom- 
valves were also present, and these showed complete resistance to 
the caustic alkali. 
The appearance of a coccolith in polarised light is characteristic. 
Between crossed nicols, the thin flange of the large valve appears 
inactive; the entire inner ellipse, on the other hand, exhibits a 
dark cross, the arms, in some cases, revealing a certain amount of 
spiral bending. A somewhat complex crystalline structure is thus 
suggested. 
That there is some organic matter present between the valves 
appears suggested by the granular appearance often presented in 
the annular chamber, embracing the central connexion, and also 
by the fact that, upon solution in dilute acid, just such a ring of 
granular particles is thrown down, and alone remains to mark the 
spot where the coccolith had been. This ring assumes a tawny 
yellow or brownish colour when acted upon by iodine. Or, 
again, if the coccolith be treated with strong /iguor iodi, the valves 
dissolve, and this ring remains as a dark granular ellipse. 
From these observations, it would appear that a ring of 
(residual ?) protoplasmic matter surrounds the central connexion. 
In many specimens of free coccoliths we have seen a slimy, possibly 
proteid, mass depending from the smaller valve, or enveloping the 
1Biitschli: Protozoa. Plate I. Wyville Thomson. The Depths of the Sea, 
p. 413 
312 
