34 JOURNAL OF CONCHOLOGY. 



ON THE MEANING OF THE GLYCOGENIC 



FUNCTION IN THE MOLLUSCA. 



A Study in Comparative Physiology. 



By Dr. J. W. WILLIAMS, M.A. 



(Read before the Conchological Society, May 2nd, 1888, and recommended for publication 

 bj' the Rev. A. H. Cooke, acting as referee). 



The substance which Claud Bernard discovered in the 

 liver-cells of the Vertebrates and the MoUusca in 1857, and 

 which is known to physiologists under the various names of 

 glycogen, hepatine, bernardine and zo-amyline, or animal starch, 

 has during recent years been discovered by several continental 

 and other workers as existing in the tissues (other than the 

 liver) of the Molluscan body, and has, by them, in the majority 

 of instances, been quantitatively estimated. It is our business 

 here to pass over in review these observations, and to try 

 if we cannot from them, and from the analogies present in the 

 animal kingdom generally, build up the superstructure of a 

 somewhat stable hypothesis as to its origin (mother-substance) 

 and its use in the economy of the MoUusca. 



Glycogen (Cg H^q O5), as can be seen from its formula, 

 is an isomer of starch and dextrin. It is a white amorphous 

 substance, soluble in water, insoluble in alcohol and ether, and 

 its aqueous solution is opalescent and has a strong dextro- 

 rotatory influence on polarised light. It can be readily con- 

 verted into dextrin by weak acids or by an amylolytic ferment. 

 Its presence in the tissues may be detected — provided the 

 animal has been recently killed — by testing with ioduretted 

 potassium with which it gives a wine-red colour, disappearing 

 on heating, reappearing on cooling. In the Vertebrates it has 

 been detected in the liver (i"5 — 4 percent.), muscles, villi of the 

 chorion, embryonal tissues, placenta, and the leucocytes of the 



J.C, vi., Jan., 1889. 



