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Show 278 DR. H. GADOW ON EVOLUTION [Mar. 20, at Oaxaca itself it was joined by the spotted, rather brightly coloured C. bocourti. Thus the Cnemidophorus-fauna showed a very different aspect in the east, south, and north-west of the triangle examined during m y first journey. On the second journey, chiefly in the States of Morelos and Guerrero, the aspect was again different. There are no Cnemidophori in the Valley of Mexico. They were not met with until I had crossed the high range of mountains which separate the Central plateau from Morelos. The only Cnemidophori at Cuernavaca were the partly striped, partly marbled or slightly cross-barred variation of C. mexicanus, var. balsas, and such specimens were traced southwards to the River Balsas and up again to Chilpancingo in Mid-Guerrero. In the hot valley of the Balsas itself it associated with C. deppei, which was, however, rather differently coloured from any of those met with in Oaxaca; it disappeared long before the backbone of the Sierra Madre del Sur upon which Chilpancingo lies; but on descending the southern slope, the upper limit of the Tierra caliente was marked by the reappearance of C. deppei, and by a larger striped form which recalled C. immutabilis, and any doubt about this was set at rest at a still lower level, where these two kinds persisted down to the Pacific coast. All this was sufficient to rouse m y interest, and I did not miss many opportunities of at least trying to secure as many of these lizards as possible. It was not easy. Only at a few places did I receive real help from the Indians. In 1902 I caught the lizards by hand, with nooses or with whips, a procedure which often reduced m y party to utter exhaustion. Shooting with a pea-rifle was naturally not very successful. In 1904 I took Dr. Meek's hint and provided myself with a small pistol and shot-cartridges, and thus I secured hundreds of creatures which otherwise would have escaped. Still, even this was hard and uncertain work. When, as in Guerrero, during the rainy season a dense mass of herbs springs up almost everywhere, no ground-lizard can be seen except in the narrow tracks across which they flit, to hide in the tangle, warned by our approach. Moreover, they are very local and they do not always appear. Rain, certain winds, or a dull sky keep them in their lairs. One may ride for days and not see a single specimen. Then suddenly there may be hundreds, and what are really members of one clan or even of a smaller family may be collected. The next few days again may yield nothing or only a single specimen here and there; and this is really woi'se than nothing, since it leaves it undecided whether its characters are truly typical of that district, or merely individual. W e collected in the States of Oaxaca, Morelos, and Guerrero some 250 specimens. An enforced prolonged stay in the hospitable house of Professor Whitman in Chicago enabled me to examine about 200 specimens in the Field Museum of Nat. Hist., mostly collected by Dr. Meek in regions which I have not visited myself, but about which he could give m e valuable information |