Morphological Variation and Its Causes in A. tigrinum 45 



temperatures. On the other hand, a broad-toed specimen, over- 

 loaded with tissue at every point, undergoes, in suitable environ- 

 ment, an easy metamorphosis in which the destructive metabolism 

 does not attack the feet at all. Figures 11 and 12, on plate II, 

 show the foot of a rapidly grown specimen, photographed in 

 nearly the same position, one before and the other after meta- 

 morphosis ; they will be seen to dififer very little in breadth of the 

 toes. On plate IV, I have again blocked out the feet of several 

 characteristic adults. Figure 6 shows the foot of a slender adult 

 nearly 19 cm. in length. Although not from the same specimen, 

 it corresponds closely to the larval foot, figure 6, plate II. Fig- 

 ures 7 and 8, of plate IV, show the very slender-toed feet of twp 

 individuals (21 and 19 cm. respectively) which had been fed for 

 about nine months in a cool basement, and wdiich metamorphosed 

 there as well. The slenderness of these toes is very evident, espe- 

 cially in figure 8, which shows the limb of what was originally a 

 very short, robust specimen. A little more rapid growth followed 

 by metamorphosis in its first season would have turned out a foot 

 like figure 9. This latter is the foot of a rapidly grown specimen 

 just after metamorphosis from a larva much like those from 

 which figures 8, 11, and 12 of plate II were taken. Contrast this 

 foot, figure 9, with that in figure 7, bearing in mind that both ani- 

 mals were photographed at about the same time after metamor- 

 phosis, that both are males as yet not sexually mature, and both 

 healthy animals attaining full sexual maturity at about the same 

 time thereafter; the possessor of the foot in figure 7 was nearly 

 22 cm. in length and that in figure, 9 but 20 cm. Another illus- 

 tration of the slender toe is shown in figure 10, plate IV. It is 

 from an adult wild male nearly 28 cm. in length, all the lines of 

 the body and head showing it to be the result of very slow larval 

 growth. 



In speaking of the feet, I have thus far considered onlv the 

 depression of the toes and the presence or absence of the cuta- 

 neous borders at their sides. It may seem like excessive attention 

 to detail to separate from this latter character the matter of the 

 webbing of the toes at their bases. None the less, I find that the 

 two characters are not necessarily correlated and are not pro- 



241 



