Page:Popular Science Monthly Volume 84.djvu/305

Rh free spine on the pectoral fins which enables them to cling tightly to the rocks; the caddis fly larvae are all fastened firmly by threads; the water bugs are greatly flattened so that when they cling to a rock their bodies offer little resistance to the water. On the surface of the brooks enormous hairy spiders with ridiculously small bodies hunt for a living.

The tree frogs in the mountains were hard pushed to find a place to breed, for there was no standing water on the ground. They either carried their eggs on their backs or laid them in the bases of bromeliads. Many of the aquatic animals which are characteristic in other parts of the world are lacking in the mountain streams. There were no snails, pill bugs, or amphipods. The fauna was a specialized one—limited mostly by its ability to avoid being swept away.

In the slow rivers of the lowlands the most characteristic animals were the shrimps and prawns which often possessed greatly elongated claws. Curious little shrimps belonging to the family Atyidæ were quite common. These crustaceans have the first two pairs of legs modified into little brush-like forceps with which they scrape the microorganisms from the soft bottom or from aquatic plants. Many land and freshwater crabs lived along the shores of the rivers. Among these Cardiosoma guahumi was most conspicuous on account of its blue color and large size. This big crab digs holes in the mud beneath the trees near the mouths of rivers. It comes out at night seeking food and climbs the trees to eat the leaves. It was a great sight to watch hundreds of these crustaceans on the mud flats, sitting motionless in the glare of the jack-light.

Along all the streams below 2,500 feet there were many lizards of the genus Basiliscus. These animals have a very long slender tail and small front legs. When disturbed they stand nearly upright and run swiftly over the surface of the water, using only the hind legs and the tail, like the ancient dinosaurs. In the trees along the rivers we encountered many iguanas. These big lizards sit in the trees and if disturbed often