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no. 16] amphibians of western north america
j 7
Breeding and Metamorphosis
Although most amphibians lay their eggs in water, certain species
depart from this rule. In western North America, the salamanders
of the genera Batrachoseps, Plethodon and Aneides deposit their
^gs in moist places in holes or caves, or under stones, logs, boards,
leaves or moss. Our other amphibians resort to the water to lay.
The number of eggs laid varies with the species and the individual,
and may range from less than a dozen to several hundreds.
The eggs are spherical and usually pigmented, at least above,
except in the species of terrestrial habit. They usually are laid
in small clusters (Triturus, Plethodon, Aneides, Hyla), large
masses (Ambystoma, Rana), or in long strings (Bufo), and are
surrounded by transparent gelatinous material. The size of the
egg does not correspond with the size of the amphibian. The eggs
which are not laid in the water are much larger than those that are.
The eggs soon develop into tadpoles or larvae with gills and
tails but no limbs. After a time, which may vary from two or
three days to as many weeks, the larvas of those species which
deposit their eggs in the water escape from the gelatinous masses
or membranes and become free-swimming. During the period of
growth which follows, arms and legs develop simultaneously. In
the Salientia the arms are hidden for some time within the gill
chambers, and after they become external they remain much smaller
than the hind limbs, while in the Caudata the arms and legs are
about equally developed. After a period of days, weeks, or months,
the aquatic larva undergoes a metamorphosis, during which it
looses its gills and, in the case of the Salientia, its tail, and assumes
the form, structure and coloring of the air-breathing adult.
In those species which lay their eggs on land, the larval stages
of growth and the metamorphoses occur within the egg membranes,
the young being hatched as small duplicates of their parents.
Collecting and Preserving
Amphibians are usually found in moist places. Many species
are nocturnal. The salamanders of the genera Triturus and
Ambystoma often are found in springs, streams, ponds, or lakes.
Other salamanders seem rarely if ever to go into water. Such
are the species of Batrachoseps, Plethodon, and Aneides, which
even lay their eggs on land. These salamanders usually are found
in moist places, under stones, boards, logs, or moss, under the