THE FROG 51 



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

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

 and there converted into glycogen, pending the demands of the general 

 tissues of the body. As occasion arises 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 by the 

 liver cells. The storage function of the liver is one of considerable im- 

 portance, especially during hibernation and at the breeding season ; the 

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

 ance with the amount of reserve food contained. The details of this 

 phenomenon have been worked out by Alice Gaule in Rana esculenta. 

 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 ex- 

 hauStion 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 dif- 

 ference 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 sper- 

 matozoa 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. 



Weight of Weight of 



Month male liver female liver 



January 10 grms: 13 grms. 



"February 10 12.5 



March ' 13 11 



April 10 10 



May 12 9 



Tune 5.5 7.5 



July 7.5 11 



August 6 12 



September 22.5 27 



October 18 25 



November 22 25 



December 18 22 



"Reserves of food are also laid up in the fat-bodies. These have no 



