SINCE relatively little information is available concerning the Ambystoma of California, it seems desirable to record certain data accumulated during the past few years, mostly incidental to the collection of embryos and adults for experimental purposes. The first observations on the spawning migration of A. tigrinum californiense were made recently by Professor W. H. Rich. During the first heavy rain of the season, on January 1, 1940, he collected approximately 45 adults between 10 and 11 P.M. on the highway bordering Lake Lagunita near the Stanford golf course. Twenty-eight of these had been killed by passing cars. The living specimens were migrating in the direction of the lake-bed, although the latter had not yet begun to fill with the winter rains. Of the dead specimens, dissection revealed that 18 were males and 4 females, with the remaining 6 too mangled for identification of their sex. The living specimens included 7 males, 8 females, and 2 immature specimens. The males were readily distinguishable without recourse to dissection by their heavily swollen cloacae and more prominently developed tail fins, Three of the larger males measured 21, 22, and 23 cm., as compared with 17, 18, and 19 cm. for the same number of females.1 The following evening, which was cool and clear, the writer visited the same half-mile stretch of road and found no animals. It was raining heavily again the next evening, January 3, however, and three excursions between 7:30 and 10 P.M. netted 15 females and 8 males. In addition, 5 or 6 injured or killed animals were observed. Two nights later Mr. L. E. DeLanney, also during a heavy rain, collected 4 females and one male in one trip along the same portion of road. The declining percentage of males in the three successive collections may or may not be indicative of a differential in onset of migration between the two sexes, which appears to be so marked for A. maculatum of the eastern United States (Moment, 1938). A striking behavior was exhibited by the animals shortly after they were placed in a large tank of water on return to the laboratory. In several instances the male was observed to pursue the female actively around the aquarium, his head beneath her tail and appearing to nose her cloacal region. On the following morning a number of spermatophores were found attached to the floor of the aquarium. Although spawning of the females did not ensue, this is possibly attributable to the crowded and unnatural conditions afforded by the aquarium. DATA ON SPAWNING