22 /. H. Powers 



than a very moderate degree of compression. Fifth, the form of 

 tail produced, both in the male and in the female, is more or less 

 unique and is vmlike anything seen in wild specimens. In the fe- 

 male, the tail, though broad and compressed as in figure ii, plate 

 V, is thick and tieshy to the tip and even on its dorsal ridge. In 

 the males it becomes much thiruier, especially at the tip (most of 

 all after attainment of sexual maturity) ; seldom is there a very 

 slight membranous dorsal border. In nearly all males, however, 

 the whole dorsum is so much thrown into folds that the dorsal 

 ridge becomes quite ruffle-like. Even the thick tails of the fe- 

 males show something of this transverse corrugation of the dor- 

 sal moiety due to the hypertrophy of this portion. Sixth, the 

 maximum breadth of tail in wild individuals is not only confined ^ 

 to the male sex but is a seasonal character present only in the 

 breeding season. I can fully confirm Baird's statement that the 

 animals are most aquatic at the breeding season, with the further 

 addition that the males are very much more aquatic than the fe- 

 males, lingering in the water, provided that food and shelter from 

 light are present, for weeks after breeding is past and the females 

 have left. These facts look as if the aquatic life of the male pro- 

 duced the caudal swimming organ ; and possibly, if we are suffi- 

 ciently Lamarckian in tendency, we may suppose that in the long 

 run such has been the case. But further observations show that 

 it is not, at present, an annual adaptation. It takes place before 

 the animals enter the water in the spring. This I have observed 

 both in wild adults caught en route to their breeding places early 

 in March, and in many adults which I have wintered in boxes of 

 earth in cellars. That it should occur, however, requires that the 

 animals should have passed the winter at a suitable temperature 

 and that they shall have been sufficiently well fed the preceding 

 season. Seventh, the whole matter of tail-form, aside from the 

 minor sexual difference, proves to be chiefly a matter of nutri- 

 tion. The tail is about the first organ to show the results of 

 undernutrition, and the occasional excessive expansions of the 

 organ in water never take place, so far as my experience goes, 

 save as a result of continued high feeding. I have found no 

 means of feeding aniblystomas to the maximum which does not 



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