The Frog 51 



to take the place of that consumed in the various life activities, and to 

 increase the size of the body. Food is stored up in the liver-cells as 

 glycogen, a carbohydrate similar to starch and often called "animal 

 starch." The absorbed food is conveyed to the liver by the portal vein 

 and is there converted into glycogen, pending the demands of the gen- 

 eral tissues of the body. As occasion rises, it is converted into more 

 soluble material, a sugar, and sent into the main bloodstream via the 

 hepatic veins and inferior vena cava. Fat globules are also contained 

 in the liver cells. The storage function of the liver is one of considerable 

 importance, especially during hibernation and in the breeding season ; 

 the weight of the organ exhibits a well-marked seasonal variation in 

 accordance with the amount of reserve food contained. The details of 

 this phenomenon have been worked out by Alice Gaule in Rana escu- 

 lenta. The breeding season of this form is in May, June, and July. 

 The table shows the average weight of the liver in the two sexes month 

 by month. 



"It will be observed that the liver is most depleted in both sexes 

 in June, the middle of the breeding season, and that it reaches its maxi- 

 mum weight in September when the system has recovered from the 

 exhaustion of spawning. Throughout the winter the reserves are being 

 steadily used up, with no recovery by the female, the average weight 

 of whose liver is greater than that of the male, but with a slight recovery 

 in March and in May by the male. It is probable that this general 

 difference depends upon the fact that the ovaries of the female make a 

 great and continuous demand upon her system throughout the whole 

 period of maturation, so that in spite of renewed feeding in the spring 

 there is no recuperation in the liver. In the male, however, there is no 

 such continuous drain but rather a sudden call upon the reserves at the 

 actual time of pairing — a call due not only to the discharge of the 

 spermatozoa but also to the muscular exertions of the male at that 

 season. This call is marked in vigor by the sudden reduction of the liver 

 to rather less than half its weight in June. 



Month 



Weight of 

 male liver 



Weight of 

 female liver 



January 



February 



March 



10 grms. 



10 



13 



13 grms. 



12.5 



11 



April 



May 



June 



10 

 12 



5.5 



10 

 9 

 7.5 



July 

 August 

 September 

 October 



7.5 



6 



22.5 

 18 



11 

 12 

 27 

 25 



November 



22 



25 



December 



18 



22 



