70 



ECOLOGY 



Part II 





Fig. 5.3. Noses are adapted to many uses in addition to smell and breathing. A 

 ground mole bores its way wedging with its nose and digging with its feet; mice 

 and other rodents use their noses as wedges; anteaters probe into anthills. The noses 

 of elephants are general tools, for shower baths, hfting logs, and picking up nuts; a 

 pig's snout is a living plow. 



Form, Symmetry and Segmentation. The symmetry of animals is the ar- 

 rangement of structures with respect to a point, a line or a plane. In radial 

 symmetry the structures are placed like the parts of a wheel in relation to its 

 center. In bilateral symmetry the right and left sides correspond to one another. 

 Symmetry is correlated with an animal's way of life, especially its lack of 

 locomotion or kind of locomotion. Hydras, corals, jellyfishes, and others are 

 radially symmetrical. Such animals move about slowly or are attached like 

 the corals. In sea anemones and starfish and their kin bilateral symmetry 

 appears within the radial; that is, the wheel or cylinder shows a division into 

 two parts. This is a persistence of the bilateral symmetry of their free-swim- 

 ming young. The majority of animals, and all the vertebrates, are bilaterally 

 symmetrical (Figs. 5.5, 5.6). They move about freely, often with great speed, 



Fig. 5.4. The relative size of the blue whale (length, 90 to 100 feet), whale 

 shark, and giant squid. All of them live surrounded by the lifting capacity of 

 buoyant salt water. The ostrich and elephant receive no such support. 



