Coccospheres and the Origin of Coccoliths. 



309 



crystalline precipitate. "\Miile this preparation was under observation, 

 dilute acid was introduced under the cover-glass, and it was foutid 

 that gas bubbles were generated in connection with the larger crystal- 

 line aggregates only, while the smaller ones dissolved without any gas 

 appearing in their immediate neighbourhood, even after the liquid was 

 completely saturated, and contained much free gas. Crystalline 

 masses having a diameter of 0*027 mm. dissolved in this manner 

 without the formation of bubbles. In the case of the solution of 

 the larger masses, an increase in size of the bubbles previously 

 existing in their neighbourhood was observable. It seems quite prob- 

 able that if greater care were taken to eliminate all free gas from the 

 water in which the crystals were mounted and from the added acid, 

 that much larger masses of calcium carbonate might be brought into 

 solution without the evolution of bubbles, as then the cohesion of the 

 liquid would have to be overcome before they could appear. To 

 overcome this would require a force of many atmospheres. In any 

 case the observation quoted shows that solid masses of calcium car- 

 bonate having the same diameter as a coccosphere, (and consequently 

 containing a great deal more calcium carbonate), dissolve ■\\dthout pro- 

 ducing free carbon dioxide. 



Besides their ready solution in weak acids, the behaviour of coccoliths 

 towards picric nigrosine is very characteristic of calcium carbonate. 

 AVhile the coccolith is dissolving in this stain a dense, dark, but 

 extremely fine precipitate or coloration is formed on its surface. The 

 same reaction may be observed in the solution of small crystals of 

 calcium carbonate. In the case of the coccolith the precipitate is most 

 marked in the D-shaped holes, round the collar connecting the two 

 valves, and along the radial strise on the valves. It seems probable that 

 the remaining parts of the valves do not possess sufficient material to 

 render the reaction apparent in their case. Besides thus affording 

 additional evidence as to the nature of the material forming coccoliths, 

 this reaction makes several obscure points in their structure stand out 

 with great clearness. 



That the coccolith is not pure calcium carbonate appears from its 

 behaviour towards a 1 per cent, solution of sodium carbonate. AVhen 

 mounted in this reagent the coccolith after a short time assumes a 

 peculiar appearance. Its surface becomes lumpy and loses its clean-cut 

 contour. Some coccoliths exhibit this change much more markedly 

 than others, and all more plainly towards their periphery than at the 

 centre. It is probable that the change is brought about by the solution 

 of the organic basis remaining over in the coccolith. The completeness 

 of the replacement of the organic basis by calcium carbonate would 

 then determine the extent of the change."*^ The same change is 



* Calcareous sponge spicules undergo a similar cliange wlien treated witli this 

 reagent. 



