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Show 1 9 0 5 .] AMPHIBIANS AND REPTILES. 2 01 which lies at an altitude of about 7600 feet, was fruitless. In the month of September 1904, however, when we revisited this district, I was able to ascertain that these Newts live regularly in the stream below Contreras (altitude 8090 feet) down to about 7900 feet, where the stream leaves the hills, and runs, still swiftly, in its stony bed through the Pedregal, or recent field of lava, then through rich evergreen meadows into Lake Xocliimilco. Moreover, I can now add with certainty that A. altamirani is absolutely aquatic throughout its life. The natives (millers, field-labour ers, and boys) knew the creatures well. They called them " axolotes sordos " (deaf, having no ears), and described them as axolotes sin aletas (without winglets, meaning gills); when I searched for them on land, on the bordering meadows, under stones, or amongst the trees, the people laughed at my ignorance of expecting to find " fishes" on dry land. There are no fishes in that stream. But this, their " fish," they pronounced as no good, because these axolotes de cerro (Mountain Axolotl) are not eaten like the " axolotes del lago." During our last visit the mountain-streams were transformed into turbid roaring torrents, and it was only at a few spots that the Newts were visible, generally in some stiller water, in the shelter of some great boulder. There they stood, or rather were lying, on little patches of sandy bottom, the larvae working their gills vigorously, the adult motionless except for the undulating tail, and never rising to the surface to breathe. They were all extremely shy, quickly hiding beneath or between the stones. In the Montes de las Cruzes, close to the railway-station Dos Rios, the streams form here and there little swamps or ditches, with much watercress in the slowly-flowing water ; there we found plenty of larvae; the adult only in the running water. Not one of these mountain-streams runs dry. The lungs are well developed. The only specimen, a larva 100 mm. long, which I succeeded in bringing home alive in 1902, metamorphosed within 8 weeks, losing the fins and gills, and closing the gill-openings completely, but it died before losing the yellow and black piebald coloration. The distribution of Amblystoma in Mexico coincides absolutely with the large central and western portion of the country, which has been covered with volcanic masses, repeatedly or successively, since the Eocene epoch ; and the last outburst, which produced the Pedregal near Mexico, is known to have occurred after this part of the country was already inhabited by man. It was impossible for Amphibia to live on such a terrain until it was weathered enough to sustain a permanent and moisture-loving vegetation._ In fact every locality where A. tigrinum is known to occur is on the Quaternary, mostly sandy, patches formed by the disintegrating debris of the volcanic masses; or it is found in the lakes, all of which are partially filled-up mountain valleys. We have to conclude that the Amblystomas are recent immigrants from the North. Where they have met such lakes, |
