354 EXPERIMENTAL GIGANTISM 



I have no other records concerning the growth of the species Amby- 

 stoma tigrinum except those afforded by the control animals of these 

 experiments. These give information on the growth during a period 

 of only 1^ years (84 weeks), the present age of the animals of Series A, 

 XL VI, and LV. Apparently this species, as illustrated in Figs. 3, 

 4, and 5, behaves very much in the same way as the species Amhy stoma 

 opacum, growth being most rapid during the larval period, and con- 

 tinuing at a fairly high rate till about the end of the 1st year, after 

 which it becomes rather slow. 



It is not so simple to determine the maximum size of this species as 

 in the case of Amhystoma opacum, since there are two races of the tiger 

 salamander, a western and an eastern one, which are very different 

 in respect to the type of growth. The western race seems to be nat- 

 urally a giant race; this is true at least for the specimens which meta- 

 morphose from the well known neotenous larvae found in the western 

 lakes. This condition, however, is doubtlessly caused by disturbances 

 of the endocrine system and is rather pathological than normal. My 

 experiments, performed with eastern animals, cannot be checked by 

 means of these giants although they are apt to throw some light on 

 the gigantism of the neotenous specimens and those that have meta- 

 morphosed from neotenous larvae. Cope in describing a large number 

 of specimens of Amhystoma tigrinum mentions that the largest speci- 

 men among them measured 10 inches (about 244 mm.) and that 

 De Kay described a still larger one measuring 11 inches (about 280 

 mm.). The largest specimen among 55 neotenous larvae which I 

 myself collected in the vicinity of Tolland, in the Colorado Rocky 

 Mountains, measured 257 mm., while all the metamorphosed specimens 

 collected in the same locality were much smaller. As pointed out 

 above, I have used in my experiments only eggs that were from 

 females of the eastern race. Unfortunately, I have not reared 

 enough animals of this species to form a conclusive idea as to the 

 normal maximum size of the species. But the largest individual 

 on record in my laboratory (one of the controls of these experiments) 

 measures 200 mm. at an age of 84 months; it is, however, still growing, 

 although very slowly. In the collection of the American Museum of 

 Natural History I found the largest specimen among the nine 

 largest animals, eastern as well as western, to measure 208.7 mm. 



