DR. T. ALCOCK ON POLYMORPHINA TUBULOSA. 249 



in the economy of the animal, this being to open free 

 communications between the internal and external sarcode. 

 As to the process by which the shell-matter is removed, 

 it seems impossible under the circumstances to suppose it 

 done in any other way than by absorption by the sarcode 

 in contact with it. Among the specimens shown is one of 

 P. tubulosa which has been completely broken open ; and 

 this shows that the process of absorption is not confined to 

 the outer walls, but that the inner partitions, which at first 

 formed parts of the walls of the separate chambers, are 

 also in great part removed, throwing the whole of the in- 

 terior into one large irregular cavity. 



The quantity of carbonate of lime deposited, at once in 

 the covering of the external sarcode and its pseudopodia, 

 is so considerable that some unusual source might natu- 

 rally be looked for to supply it ; and this is apparently 

 found in the shell-material redissolved by the process just 

 described, which must eventually lead to the sarcode being 

 excessively charged with mineral matter, and may be con- 

 sidered a sufficient reason for the final catastrophe ; and if 

 the view here given of the later stages of the life of Poly- 

 morphina tubulosa be correct, it adds another point of in- 

 terest, by showing that the deposit of shell-material, in 

 this one case at least, is more of a chemical than a vital 

 act. 



SEB. III. VOL. III. 



