ii HABITS AND NATURAL HISTORY OF THE FROG 35 



relation to the rest of the body, according to Langendorff, 

 Ploetz, and Funke, even increases during the winter months. 

 After the breeding season the minimum size is reached, after 

 which there is a gradual increase during the summer. 

 Apparently, therefore, there is either a growth of the liver 

 during the winter at the expense of the rest of the body, or 

 the various other organs decrease more rapidly than the 

 liver in size. 



The blood of the frog undergoes in the spring, after the 

 animal has begun to take food, a rapid regeneration, a pro- 

 cess which in higher animals takes place at all times of the 

 year. There is a great increase in the number of blood 

 corpuscles, both red and white. The marrow of the bones, 

 where the new blood cells are mainly produced, shows in the 

 spring a lymphoid structure, becoming more and more fatty 

 toward fall, after the production of new blood cells has 

 mainly ceased. 



The changes in the fat body at different times of year have 

 been studied by Ploetz and Funke, both of whom found 

 in the two species studied {Rana temporaria and Rana 

 esculentd) that this organ changed but little during the 

 winter months, but suffered a marked diminution in size just 

 before and during the breeding period in the late spring. 

 After this there is a gradual increase in the size of the fat 

 body until fall, when it reaches its maximum. 



The advent of the breeding season is marked by great 

 changes in the reproductive system, both in the gonads, or 

 organs which produce the sex cells, and the various accessory 

 organs. The variation in the size of the ovary before and 

 after the discharge of the ripe ova is enormous. After the 

 eggs are laid in the spring, the ovary shrivels to a small 

 fraction of its previous dimensions. During the summer it 

 increases in size, and in the fall it may fill most of the body 



