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University of California Publications in Zoology [Vol. 27 
It is abundant in Tucson and on the University campus. One usually sees the 
toads a few days before the beginning of the summer showers, and their presence 
is taken as a sign of rain. Seldom does one see them during dry periods. They 
may, however, be observed about irrigation ditches and in irrigated land any time 
during the growing season. 
With the first heavy summer showers, as a result of which water will stand 
in pools, these frogs [sic] appear in abundance and lay eggs which hatch very 
soon; the young pass in a remarkably short time through the tadpole stage. 
I do not think it is more than a month ’s time from the egg stage to the time when 
the young toad hops away with his tail nearly absorbed. 
One particular specimen 
was collected in Sabino Canon, St. Catalina Mts., in June (about the 15th), 1903. 
A small stream of water came down from the mountains as the result of rain 
above, and these toads appeared in abundance, pairing almost immediately. On 
that day every female was laying eggs. The eggs were laid in the clear stream of 
water, which was perhaps a foot to eighteen inches deep. I assure you there was 
no lack of noise that day or night, the croaking being incessant. I have also seen 
it at Oracle, Ariz., where it gets into the sheep troughs and causes more or less 
trouble. 
The life-history in relation to the environment . — This species is 
distinctive among' the Salientia of North America (north of Mexico) 
in being the largest species of Bufo found here and at the same time 
being restricted in general range to the hottest portion of the conti- 
nent. So far as known, however, it does not inhabit the desert proper 
but is to be found only in localities where the water supply is perma- 
nent as along large rivers or in irrigated districts. Furthermore, it 
departs from the typical habits of the toads (Bufo) in being semi- 
aquatic. Three other species of Bufo inhabit the general territory 
occupied by alvarius ; of these, punctatus is of small size and can there- 
fore find safe shelter in small crevices adjacent to seepage or about 
springs; cognatus and woodhousii are possessed of tough roughened 
skins which probably resist desiccation ; being of ‘ average ’ toad size 
they can probably find suitable shelters just as do toads in more 
temperate regions, and they have enlarged metatarsal tubercles suit- 
able for digging. Alvarius is of such large size that an adult would 
probably experience difficulty in securing shelter in the usual bufonine 
way, were it of terrestrial habit. But by assuming a semi-aquatic 
mode of life and restricting its range to the neighborhood of perma- 
nent streams, it greatly reduces the danger of desiccation. With the 
bufonid protection of parotoid glands, which, probably by reason of 
the poisonous nature of their secretion, confer an unusual measure of 
safety upon the individual, in combination with aquatic habits, a basis 
