Chap. 5 



ANIMALS AND THEIR ENVIRONMENTS 



75 



Fig. 5.9. Hosts of animals cling to the rocks and seaweeds between the tide lines. 

 Common rock barnacles (Balaniis balanoides) {above), and edible periwinkles 

 {Littorina litorea) {below). Periwinkles are about the size of cherries. In British 

 shore resorts "winkles" are roasted and sold like peanuts in America. (Photograph 

 by D. P. Wilson, Marine Biological Lab., Plymouth, England.) 



of these live upon one another and the oflspring of one another (Fig. 5.11). 



Salt water is a far better support and carrier than fresh water. The eggs of 

 marine animals float easily; those of fresh-water animals often drop to the 

 bottom, are attached to vegetation, or carried about by the parent. The young 

 ones climb, creep, and hold onto whatever comes their way. 



Ponds and Lakes. Healthy ponds and the coves of lakes usually hold 

 goodly populations; in midsummer they teem with them (Figs. 5.12, 5.13). 

 Ponds are smaller than lakes. They are defined as bodies of water so shallow 

 that green plants can grow attached to the bottom even at the center. Lakes are 

 too broad and deep for this. Near the borders of ponds and the protected 

 shores of lakes the plants are food depots and shelters for invertebrates, snails, 

 climbing fingernail clams, innumerable crustaceans, and aquatic insects. There 

 are a few resident vertebrates, chiefly frogs and turtles. The plants have partly 

 or completely submerged stems — blue-blossomed pickerelweeds, arrowheads, 

 rushes, and waterlilies. All of their stems are coated with green algae and bac- 

 teria (Fig. 5.14). Yellow perch, bass, and pickerel come among them to 

 forage. 



