30 SCHMIDT OX THE COMPARATIVE PHYSIOLOGY 



In 100 parts of the incombustible residue — 



AnoJonta. Helix. 



Carbonate of lime .... 99-45 99-06 



Phosphate of hme .... 0-55 0-94 



We have here scarcely any process of cell-formation, mere 

 amorphous, hardened mucous masses (albuminates) separated by 

 calcareous layers, and scarcely any phosphate of lime ; the coin- 

 cidence is so striking that we cannot avoid regarding it as a con- 

 firmation of the view of the physiological import of this salt 

 proposed above. I believe, as already stated, that a definite 

 combination of albumen with phosphate of lime, or rather, that 

 an albuminous solution saturated with a certain portion of the 

 latter, possesses the power of condensing into comparatively solid 

 membranes around heterogeneous bodies when brought into 

 contact with them, i. e. of forming the wall of primary cells. 

 However, I have not yet succeeded experimentally in ascertaining 

 the "why" and " wherefore " with sufficient accuracy. Before 

 we leave the Mollusca, I shall say a few words on the physiolo- 

 gical import of the folds of the mantle in Anodonta and Unio, 

 which is very interesting. 



This mantle consists of an intermediate scanty layer of fibrous 

 tissue, resembling cellular tissue, which is covered internally by 

 ciliated epithelium, but next the shell by the so-called glandular 

 epithelium, i. e. epitheUal cells containing nuclei, and resembling 

 tiie cells of the liver. Now whilst the former has constantly to 

 supply the gills with fi-esh water, the function of the latter is 

 evidently that of decomposing the blood, of secreting a compound 

 of albumen with lime next the shell, which is decomposable even 

 by the carbonic acid of the air or of the water, but of retaining 

 the phosphate of lime and returning it to the organs which re- 

 quire it for the process of cell-formation (testicle and ovary). 

 This view appears to me to be supported by the following facts : — 



0*7745 of the folds of the mantle of Unio, after careful sepa- 

 ration, when d.'ied at 248° F. left 0-136 of ash, containing 0- 1 1 5 

 phosphate of lime. 



0-610 of the same from Anodonta gave 0*112 ash, containing 

 0-091 phosphate of lime. 



Hence, in 100 parts of the folds of the mantle, — 



