80 



GENERAL EVOLUTION. 



The successional acceleration or retardation in metamorphosis 

 may be best illustrated in certain tailless batrachians, by the fol- 

 lowing tables. These are taken, it will be remembered, from the 

 Bufonidse and Hylidse as examples of '^ exact parallelism " ; three 

 are now added from the Eanidae and Discoglossidae. The case of 

 ^' inexact parallelism " is that of the Scaphiopodidae. 



Whether they are cases of acceleration or retardation can only 

 be determined by reference to the paleontology of the respective 

 groups, or a careful comparison of times of metamorphosis. In 

 the case of the Discoglossidae I suspect it to be retardation, as the 

 highest genus is extinct. The others I shall arrange with them 

 for temporary conyenieuce. Were I dealing with a group of Ga- 

 noids, I should imagine the process to be retardation, as this 

 group is going out of existence. On the other hand, were they 

 higher Oscine birds, we might imagine the case to be reversed. 



Assumed, 

 140th gen. 

 120th gen. 

 100th gen. 



80th gen. 



60th gen. 



40th gen. 



20th gen. 

 1st gen. 



p >-s 5 c> rj «i 2 



« >-^ 3 g. O .°° g" 

 P' £S r^ — CO H 



3 t:- 



CO a 

 of 





o 



O ffi „ 



P-S.S 



IX ^ 



■ ^ 



o 



CO 



o 



W 



s 



o 

 ■-1 



SS 



-I 



o 

 o 



O CO 



►c P 

 •s "*• 

 C 3- 

 P- 

 3 

 o 

 o 



Fig. 3. 



o 



Pi 



ft y< 



P 00 



p 22. 



Q CD 



p o 



orq 



ft 



1-1 



o 

 & 



3 

 ft 

 ft 



Ixalus. 



i 



Rhacophorus, 



Polypedates. 



No vera, teeth. 

 Sometimes " 

 Always " 



^ 2 

 §1 



P 



ft 



Points not attained. 

 Fig. 4. 



* A parotoid gland of small size is added here, but is not generic as compared with Bom- 

 binator, as the latter has collections of crypts on the same region and over the body. 



