252 PHYSIOLOGY OF THE INVERTEBRATA. 



organisms ]5umped enormous quantities of sea-water through 

 tlieir bodies so as to be able to separate out a sufficient 

 quantity to form their shells and skeletons.* But there is no 

 doubt that we have a correct explanation in the reactions 

 indicated above which have been so ably investigated by 

 Murray and Irvine. " In higher animals, like hens, the 

 carbonate of lime is secreted from the blood ; but in coral 

 polyps, in which there is no true circulatory system, and 

 where the animal is immersed in the sea water, it is most 

 probable that the reaction above referred to — the formation 

 of carbonate of ammonia — is in every way advantageous to 

 these lime-secreting organisms, and facilitates the deposition 

 of carbonate of lime by the protoplasm. In the case of all 

 the lower classes of lime-secreting organisms this change in 

 the constitution of the lime salts may take place within the 

 tissues of the animals." In fact, Murray and Irvine have 

 shown, in their experiments with oysters, that " the excess of 

 carbonate of lime observed in the liquor or diluted lymph 

 was clearly due to the decomposition of the sulphate of lime 

 in the sea water by carbonate of ammonia secreted as such 

 by the protoplasm of the animal." 



It may be stated that when sulphate of lime, urea, and 

 water are heated together to about 8o° F., carbonate of lime 

 and sulphate of ammonia are formed : — 



CaSO, + CH,N,0 + 2K,0 = CaCO, + (NH,),SO^. 



It is possible that the excretions of marine Invertebrates, 

 as well as those of the higher animals, ultimately yield car- 

 bonate of lime and sulphate of ammonia due to the action of 

 the sulphate of lime in sea water. 



(A) Murray and Irvine have also shown that the rate of 

 solution of dead carbonate of lime shells and skeletons by the 

 action of sea water " varies greatly according to the conditions 

 in which these dead remains are exposed to the solvent 

 power of the water." The following table gives a few of 

 their results : — 



* Bischof's Chemical and Physical GeoJof/y, vol. i, p. i8o. 



