688 THE AMERICAN NATURALIST. (VoL. XXXIV. 
unrelated genera and families. In these cases protection of 
some sort is generally afforded to the young, or else they have 
become adapted to an unusual environment. As a result, 
modifications in the young have been produced, as well as 
changes in the instincts and even in the anatomy of the 
parents. Examples among fish are the various cases of nest 
builders among teleosts ; the cases of Bagrus, of the siluroid 
Chromis, and of other fish that carry the young in the mouth 
for a longer or shorter period ; the case of Aspredo levis, in 
which the female carries the eggs and young attached to pedi- 
cels on the abdomen; the cases where the male fish is pro- 
vided with a temporary or permanent pouch for the young, 
and the cases of partially or entirely viviparous forms among 
teleosts and selachians. Examples among Amphibia are the 
viviparous salamander ; Plethodon and Autodax, which lay 
their eggs on land; Desmognathus, Amphiuma, and the 
Coecilia, where the eggs are laid in damp places and are sur- 
rounded by the parent's body ; and a number of Anura, which 
are the subject of the present paper. For the sake of com- 
parison with what is to follow, the salient points in the devel- 
opment of the common frog may be briefly stated. The eggs 
are laid in large numbers in water, where the larvae develop. 
The newly hatched tadpole adheres at first to a fixed object by 
means of an adhesive gland, but after a few days it becomes 
free-swimming. It possesses at first external gills; these are 
replaced by internal gills, covered by the characteristic oper- 
culum ; the internal gills are in turn gradually replaced by 
lungs ; in the mean time the hind legs and later the fore legs 
develop ; the tail is absorbed, the shape and position of the 
mouth are changed, the larval * mouth-parts" are cast off, 
and the characteristically coiled intestine is shortened. The 
metamorphosis transforms the aquatic larva into the adult air- 
breathing form. 
This general account is true for all the common frogs and 
toads of North America and Europe, with the exception gt 
Alytes. The Anura of other regions, especially 1n the 
Tropics and the Southern Hemisphere, far from having unk 
form breeding habits and one mode of development, vary 
