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Show 2 0 0 DR. H. GADOW ON MEXICAN [June 6, interesting that these burrowing, slowly moving worm-like creatures have managed to travel over at least 1500 miles of ground, covered with humus, since the close of the Miocene epoch, i.e . since the separation of the Antilles (cf. p. 237). A not unreasonable computation of one million years carries us back into the Miocene epoch. The rate of spreading could in this case have been extremely slow, only about one mile in 700 years, and this works out at three yards a year. Of course this is mere speculation, but it may be as well to give even such an imaginary instance of slow spreading. The fact remains that Dermopliis has done it, and whether we double or treble the rate of progress, or increase the time two- or three-fold, the result remains within very reasonable possibility. U r o d e l a . The Amblystomatince are a pre-eminently Eastern Pakearctic group; only two out of eight genera occur in North America: Dicamplodon ensatus in California, and Amhlystoma, with some 16 species, on the North-American Continent, and one, A. per simile in Siam. In Mexico only two species occur. Amblystoma tigrinum, the larval form of which, when permanent, is the famous Axolotl. This species has an enormous range, from the State of New York to Dakota and Colorado, whence, apparently now with wide gaps between, it extends through Mexico, as far south as the valley of Mexico City. But its distribution in Mexico is, at least now, restricted to the western Sierra Madre and the southern part of the Mexican plateau. Well-ascertained localities of this species are the following :- West of Chihuahua Town; West of the town of Durango; Cumbre de los Arrastrados in Jalisco; somewhereN.W. of Guadalajara ; district of Autlan in Jalisco ; Lake Patzcuaro in Michoacan, Valley of Mexico, notably Lakes Xochimilco and Zumpango (but not Lake Texcoco, to which alone Weismann's dismal dream to account for the permanent Axolotl stage could apply!). Possibly there are Amblystoma, either metamorphosing or as Axolotls, in or near some of the other lakes of Michoacan and Jalisco, but they have as yet not been recorded from Lake Chapala ; and I found none in the Lakes of Zapotlan; nor were such creatures, or even the name Axolotl, known to the natives. A . altamirani.-This species, which metamorphoses regularly into a gill-less Newt, is known only from the streams of the mountains which border the western and south-western side of the Valley of Mexico. It was discovered in the Montes de las Cruzes, about 15 miles to the west of Mexico City, at an altitude of 8800 feet. In 1902 I found it also above Contreras, in the Sierra de Ajusco, some 12 miles south-southwest of the city, at an altitude from 8500 feet upwards to 8800 feet. Further up the rivulets are apparently too small. 1 stated in ‘ Nature,' Feb. 5, 1903, that searching in the streams only a little above the City of Mexico, |
