AMPHIBIA 209 



Some species of frog go through to metamorphosis in a few weeks, 

 others require months, and some require two or three years. 



4. The Period of Adolescence has not been very fully studied. 

 It is a long, slow process involving changes in the relative proportions 

 of the parts, elaborations of the histological structure, and ossification 

 of the cartilaginous skeleton. The most significant changes are those 

 that are last to take place, namely, those that have to do with the 

 onset of sexual maturity. Shortly before the beginning of the first 

 breeding season, the cells of the ovaries and testes begin the processes 

 known as ovogenesis and spermatogenesis, that constitute the chief 

 features of the first period considered in this brief life history. Hence 

 we have completed the cycle for one generation. 



