332 



LOWER VERTEBRATES. 



arched roof. In ITortli America the genus Spea occupies the lowest position. Its 

 species inhabit the western part of the continent, extending to the valley of Mexico, 

 and are remarkably adapted to an ai-id climate by the great rapidity of their meta- 

 morphosis. On the occurrence of a rain during the summer, they emerge from their 

 subterranean retreats, and deposit their eggs in the pools which collect in the dry 

 arroyas, and in the low lands. Here the larvae are soon swimming about, and early 

 acquire their legs, so as to escape from the muddy fluid as soon as possible. When 

 completely changed, the young of the Spea hammondii are not larger than those of 

 the common toad. I made the following observations on the S. horribifrons which 

 I found in Idaho Territory in a region rather less arid than that inhabited by 

 S. hammondii: — 



" In Idaho, near latitude 43° 30', is situated a body of water known as Market 

 Lake. Its extent is variable, for it is said to be dependent for its water supply on the 

 overflows of the Snake River, which is a few miles distant to the eastward. An old 

 channel leads from the river to the lake, giving probability to the- statement. At the 



Fig. 199.— Ceratophrys fryi, from Brazil. 



time of my passage through the region, the water was unusually high, for a portion 

 of the stage road, with parts of numerous telegraph poles, was submerged. The lake 

 appeared to be about ten miles long by six in width. The country surrounding it is 

 arid, and the sand which represents soil rests on a basis of lava. The stage halted 

 for a short time to enable me to examine the shore of the lake. I found it to be 

 lined with a wind-row of grasshoppers ( Caloptenus spretus) which had fallen into the 

 water and been washed up, some living, others dead. Among them I found numerous 

 large fat larvae of Spea bomMfrons, occupying small spaces which they had cleared, 

 quite out of the reach of the water. Their limbs were nearly fully grown, while their 

 tails had suffered no absorption, and their jaws were toothless and cartilaginous; 

 some quite larval in form, others with wider gape. They were engaged in eating the 

 grasshoppers, and I detected several specimens with .the entire insects in their mouths. 

 In some instances, the grasshoppers' bodies were too large, and projected from their 

 mouths. These precocious larvffi were evidently air-breathers, and hopped about, 



