40 



/. H. Poivcrs 



)f animals employed 



velopment of the head, out of about a sec 

 in the experiment, is shown in figure 2, plate VI. The head of 

 this animal looks abnormal, yet it developed from an ordinary 

 small adult and showed no . signs of pathology. It was not an 

 excessive feeder. 



The flattening- of the head, although conspicuously present m 

 enforced aquatics, is not well shown in my figures, most of the 

 side views being either of individuals which showed this char- 

 acter but moderately, or else the profiles are not taken at the 

 proper angle to show the character fully. Figure 4, plate V, 

 however, shows it well considering that the specimen is an ex- 

 cessively full fed and robust individual. It had doubled or prob- 

 ably trebled its size during its year or more of aquatic life as an 

 adult. A comparison of this head with the profile outlines given 

 for the different species of the genus by Cope in his Batrachia 

 of North America will show how unlike these aquatic profiles 

 are to those of any of the species described by him, with the pos- 

 sible exceptions of A. copcannm and A. xiphias. Both of these 

 aberrant types are species founded, it would seem, upon single 

 specimens only, and present, I think, no character that I can nor 

 duplicate from A. tigriiium. either wild or modified by experimen- 

 tal conditions.^ These characters of depressed and broadened 

 head suggest at once certain lower and more aquatic genera ; the 

 truncated muzzle does the same, although this is of more general 

 occurrence in several families. This latter character is chiefly 

 interesting as showing that the adult and the larva (so called) in 

 this species are subject to parallel variations. Figure 3, plate 

 IV, and figure 2, plate VI, both show this slight truncation of 

 the head, induced by the life of the adult in water. In order, 

 however, to avoid the possibility that this delicate character has 

 been augmented or reduced bv the process of preparation of the 

 plates, which involved cutting out the photographs, I have added 

 two adult heads merely blocked out — figures 4 and 5 on plate VI. 



^The writer does not wish this statement to be construed as a final judg- 

 ment in rejection of the species in question. Such a judgment should be 

 pronounced only after a study of the type specimens themselves. It seems 

 probable, however, that a fuller knowledge of the variation of A. tigrinitm 

 will degrade not only these two species, but at least two others as well. 



236 



