OF THE INVERTEBRATE ANIMALS. 29 



cent, of nitrogen. Of the structureless membrane which re- 

 mained after treatment with acids, — 



0-165 dried at 248° F. gave 0-0195 ash =11-82 per cent, (the 

 above-mentioned silicates). 



0-261 substance gave 0*554 ammonio-chloride of platinum 

 = 15-11 per cent, of nitrogen. 



Thus both essentially belong to the same class of substances 

 (muscle, cellular tissue). The same appHes to the naked Mol- 

 lusca ; for 0-311 of the folds of the mantle of Limax, purified by 

 exhaustion with water, alcohol and aether, and dried at 248° F., 

 left 0-0] 4 ash, for the most part consisting of phosphate of lime 

 = 4-5 per cent. 



0-367 of the same gave 0-837 ammonio-chloride of platinum 

 = 15-00 per cent, of nitrogen. 



Nothing can be done with the MoUusca which live in water 

 {Limnceus, Planorbis and Paludina), as they are covered with a 

 complete fauna and flora of microscopic forms {Bacillarice and 

 Confervce). On the other hand, in Helix (jwmaiia, nemoralis 

 and hortensis) we find the inner layer of the calcareous shell 

 composed of a transparent structureless membrane, upon which 

 in the embryo the earliest calcareous layers are formed : it may 

 be easily isolated by extracting the carbonate of lime with dilute 

 acids. 



0-203 of it (in Helix nemoralis) dried at 248° gave 0-0032 ash 

 sl-58 per cent. 



0-289 of the same [Helix nemoralis) dried at 248° gave 0-692 

 ammonio-chloride of platinum =15*27 per cent, nitrogen. 



The wide difference between the cutaneous system of these 

 families and those of the Articulata is evident. We shall stop 

 a moment at the calcareous shells, and examine the proportion 

 of the carbonate to the phosphate o][^lime. 



3-486 of the shells of Anodonta, dried at 248° F., when heated 

 to redness, left, on deducting the carbon remaining after the 

 solution of the inorganic matter, 3-434 incombustible residue, 

 which contained 0"019 phosphate of lime. 



1-831 of the shells of Helix (nemoralis) left 1-760 incombus- 

 tible residue, containing 0-0165 earthy phosphates (lime with a 

 trace of magnesia). Hence — 



Anodonta. Helix. 



Structureless membrane . . 1*49 3*88 



Incombustible residue . . 98-51 96-12 



