ON THE ORIGIN OF GENERA. 



81 



u 



a OB 



% 



Pi 

 O 



OS 



EC 



be 



o 





CD 



a, 



Death. 



Eeprodiic- 

 tion. 



Tail lost (re- 

 tard.). 



Temp, roof 

 (ace). 



Ossif. front 

 (ace). 



Hatching. 



6 



M 



PR 



\ 



\ 



\ 



\ 



Reproduce. 

 Prefrontals unit. 



Ethmoid oss. 

 Tail lost. 



Frontak 0B8i£ 



p. 



o 



e 



a 



Hatched. 



In the preceding diagrams each horizontal cohimn represents 

 the life history of the individuals of each genus. The line of 

 dots, stars, etc., represents the same developmental stage of each, 

 as it appears earlier or later in the life of the individuals. The 

 point of crossing the breeding period is that at which the charac- 

 ter is rendered permanent. When the change falls on this period 

 the character is not generic, as in Ixalus, Fig. 4. The period of 

 losing the tail, like that of breeding, is represented as occurring at 

 nearly the same time in the history of every genus, as it is gener- 

 6 



