202 DR. H. GADOW ON MEXICAN [JuHC 6, 



these have become, or are becoming, too attractive for them, with 

 the result that A . tigrimtm has sunk, or is sinking, into a more or 

 less perennibranchiate state, the Axolotl. Typical Axolotl are those 

 of Lake Xochimiico, the condition of Avhich I have described in 

 'Nature,' Feb. 5, 1903, and Lake Patzcuaro, which, with its 

 rushes, weeds, and other abundance of vegetation, is very similar 

 to the Mexican lake. Sexually ripe Axolotl are also known from 

 Jalisco mountain tarns or lakes, and lastly from St. Mary's Lake, 

 Estes Park, Colorado. It is therefore the combination of certain 

 favourable circumstances (permanence of water, abundance of food, 

 shelter, equable temperature) which produces the " Axolotl." 

 Whoever has seen the veiy diftei-ent conditions prevailing in Lake 

 Zumpango, to the north of Mexico City, will easily credit Yelasco's 

 statement that A. tiyrinum metamorphoses into the normal gill- 

 less Newt, as it does in the United States, and probably in various 

 other parts of Mexico. 



All the more interesting is the fact that the other species, A . 

 aUamirani, the only one which lives in the streams of recent 

 volcanic mountains, has been modified into a gill-less but 

 permanently aquatic foiiii. 



DesmognathiNjE. — The three species of Desmognathus inhabit 

 the Eastern United States. 



Typhlotriton sj^elceus is restiicted to subterranean caves in 

 Missouri. TJiorius 2^6nnatul'its, the only lemaining member of 

 this small group, and its sole representative in Mexico, points 

 thei-efore unmistakably to the Eastern half of North America as 

 the original home of the group, not of Tkorius itself. 



This tiny Newt, less than two inches in length and thinner 

 than a match, with weak limbs and reduced digits, shows a peculiar 

 dimorphism of the size of the nostrils. They are very large and 

 open in the males, much smaller in the females. The lungs are 

 quite aborted as in Desmognathus and Bpelerpes. 



Thorius has a very limited distribution. It was discovered 

 on the south-westei'n slope of the Pic of Orizaba. I found 

 TJiorius in abundance on the south slope, 9000-10,000 feet, in 

 high, mixed forest, either on the ground beneath flat pieces of 

 fallen bark, or on decaying logs of pine between the bark and 

 the wood amongst the " worm-meal" of boiing beetles and maggots. 

 Again I met them under exactly the same conditions on the 

 Cerro de San Felipe, 8250 feet, near Oaxaca. These are the only 

 two localities so far as we know at present. It is doubtful 

 whether their distribution is now continuous ; the watershed 

 between the Atlantic and Pacific, to the west of a line drawn from 

 Orizaba to Oaxaca, averages about 8000 feet in height, and it is well- 

 wooded, but there are several deep transverse depressions in it. 



PLETHODONTiNiE. — This group, consisting of 5 genera with 

 about 40 species, is entirely American, with the sole exception of 

 Spelerpes fuscus in Europe. 



