202 DR. H. GADOW ON MEXICAN [June 6, 
these have become, or are becoming, too attractive for them, with 
the result that A. tégrinwm has sunk, or is sinking, into a more or 
less perennibranchiate state, the Axolotl. Typical Axolotl are those 
of Lake Xochimilco, the condition of which I have deseribed in 
‘Nature, Feb. 5, 1903, and Lake Patzcuaro, which, with its 
rushes, weeds, and other abundance of vegetation, is very similai 
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 very different conditions prevailing in Lake 
Zumpango, to the north of Mexico City, will easily credit Velasco's 
statement that A. ¢igrinwm metamorphoses into the normal gill- 
less Newt, as it does in the United States, and probably in various 
other parts of Mexico. 
Allthe more interesting is the fact that the other species, A. 
altamirani, the only one which lives in the streams of recent 
voleanic mountains, has been modified into a gill-less but 
permanently aquatic form. 
DESMOGNATHIN#.—The three species of Desmognathus inhabit 
the Kastern United States. 
Typhlotriton speleus is restricted to subterranean caves in 
Missouri. Thorius pennatulus, the only remaining member of 
this small group, and its sole representative in Mexico, points 
therefore unmistakably to the Eastern half of North America as 
the original home of the group, not of Thorius 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 Spelerpes. 
Thorius has a very limited distribution. It was discovered 
on the south-western slope of the Pic of Orizaba. J found 
Thorius 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 boring 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. 
PLETHODONTINH.—This group, consisting of 5 genera with 
about 40 species, is entirely American, with the sole exception of 
Spelerpes fuscus in Kurope. 
